The genial heart surgeon wanders through the shell of a two-storey building and stops in the doorway of a stark rectangular first-floor room. Cooking pots, rubble and workmen's clothes litter the floor; bare windows stare out across dirt tracks and arid farmland.
'This will be the operating theatre,' Dr Hasnat Khan says with a proud smile, before turning to the architect and the senior British nurse accompanying him to pore over plans and discuss the layout and where medical teams should scrub up before surgery.
The idea of a modern hospital with a cardiology unit here, in one of the poorest parts of rural Pakistan, seems as incongruous as a goat farm in downtown Islamabad. But despite its ramshackle appearance, the country's first charity-run hospital with a heart unit is just months away from opening. By the end of the year, it should be carrying out life-transforming surgery, in particular on poor children whose families cannot afford treatment elsewhere.
The hospital is slowly taking shape amid a cluster of tiny villages off the lorry-choked highway from Islamabad to Lahore, some 30 kilometres from the town of Jhelum, the boyhood home of Khan. Its opening will make reality a dream that cardiologist Khan has nurtured for decades and that he once secretly shared with the world's most famous woman.
Khan, who for the past 20 years has worked in hospitals in and around London, was the lover of Princess Diana - the man she called her 'Mr Wonderful' - for the last two years of her life. A discreet and fiercely loyal figure, Khan is seen as the great love of Diana's life after her marriage to Prince Charles broke down and, since her death, has arguably proved himself the most - perhaps only - honourable man to have shaped her final years.
In a rare interview, the 53-year-old Khan speaks of his determination to make a contribution for the good in his home country - and his continuing loyalty to Diana's mission and vision even after the unhappiness that marked the end of their relationship.
THEY CAME FROM DIFFERENT worlds. He was a dashing young surgeon working under Magdi Yacoub at the Royal Brompton Hospital and she was the world's most photographed woman and mother of the heir to the British throne. They met when Diana was visiting a friend who had undergone heart surgery and for the princess, the attraction was instant.
They tumbled into an intense two-year affair during which Khan was smuggled into Kensington Palace to see her, and Diana enjoyed nights out in disguise in London pubs with the doctor. The affair ended just weeks before her death in a Paris underpass alongside playboy Dodi Fayed, in August 1997.
Diana visited Pakistan, studied the Koran and spoke to Khan about a new life together overseas as the media storm that surrounded her intensified. Their relationship, it appears, broke down at least partly because of her frustration at Khan's inability to commit to her.
One plan they talked of was setting up a hospital together in Pakistan. As the 15th anniversary of Diana's death approaches and as work continues on a film about the romance between the princess and the cardiologist, Khan is preparing to leave Britain to make that dream a reality - albeit alone.
'Diana would have been involved in this - absolutely,' Khan says. 'It wouldn't have mattered whether we were together or not. She was one of those people who didn't just talk about things. She was proactive. She would go out and get it done.
'I think this hospital would be 10 years old by now if she were alive. But it's never too late.'
When Diana and Khan spoke of the future, 'it was a kind of thought process', he says. '[We thought] it would be great to set up a hospital in Asia, in Pakistan, and also to provide support services for women.'
Diana was particularly keen to work for women's rights and to help rape victims.
'My side was to build a hospital, basically,' he says.
The reason they never took their plan forward during the princess' lifetime was also one of the reasons their relationship eventually unravelled: Diana could not leave Britain because she could not bear to be apart from princes William and Harry.
'She couldn't have lived in Pakistan at that time,' he says. 'Her children were too young and she couldn't leave.
'Obviously she couldn't live in two places at the same time, spend-ing a month here or a week here and a week there. Now that William is married and Harry is grown up, she wouldn't have had a problem with it. But at the time, that was the main issue. Obviously, you don't expect her to leave the boys behind, and the boys couldn't have left the UK anyway.'
As he talks, the affection and respect Khan feels for his former lover is clear. Asked why their affair ended, he says: 'It was the non-progression of the relationship. My problem was the media. I couldn't have handled having people follow me around all the time. Maybe in time people get used to that kind of thing. I don't know. But I found that I got a lot of intrusion. You walk out of the door at any time of the day and there are people taking pictures or phone calls.
'Here in Pakistan, we would have had no problem. But I think mainly the problem was that even after two years, the relationship wasn't leading to a meaningful progression or conclusion, and that was the main stress on both of us.
'Everyone wants a relationship to be going somewhere.'
After his relationship with Diana ended, Khan had an 18-month arranged marriage with 29-year-old Hadia Sher Ali, the daughter of a noble Afghan family. He then fell in love with Greek heart doctor Alexandra Panagoulas, who is 21 years his junior.
The couple got engaged in 2009 but by last year, as Panagoulas moved to Scotland to pursue her career, their relationship had cooled and the engagement was called off.
'I had completed my training and I had a permanent job and I was settled in one place,' he says. 'She was starting her training so had to be in different parts of the country. We tried to see each other at weekends but then I would be on call and couldn't come up. Slowly, it took a strain on the relationship.
'It was purely because we were at two different stages of our professional life. She is quite ambitious and that's fair enough.'
Ironically, the relationship seems to have faltered for some of the same reasons as that with Diana, only this time the roles were reversed.
'Before, it was very different. I was too busy,' he says. 'I was trying to get a training position and to do research. And you think, 'When I've finished this, there's plenty of time.' That's why I can't sit down and say, 'Don't pursue your career', because I was like that.'
They remain good friends, however, in the way you suspect Khan maintains his friendship with all of his former partners. 'I know all her family,' he says. 'At Easter, which is a big thing in Greece, I phone up and say, 'Happy Easter.''
'I definitely still hope to marry,' he says with a smile. 'I don't know if it will happen when I come back to Pakistan. You hope for the best. My mother is always looking and always organising things. I would love to have kids.'
Whatever happens, his life in Pakistan will be dramatically different to the one he has led for the past two decades in Britain.
'It is very simple to live here,' he says. 'My [family] home is just down the road so I will have no rent to pay. Necessities and food are very cheap. If you look out from the hospital you see open countryside with cows and camels. There are no taxis or cars or buses. People walk for miles and miles just to see someone.'
Khan plans to take unpaid leave - a sabbatical of 12 to 18 months - from his position at the National Health Service hospital in Basildon when he first moves back to Pakistan but believes he may stay for good if the project is a success.
The Abdul Razzaq Welfare Trust Hospital in Badlote village, where Khan's heart unit will be based, will treat for free patients who are too poor to afford even the transport fares to the nearest town hospital, let alone surgery costs. Those patients will include a high percentage of children in an area where rheumatic fever is common, leaving many youngsters with narrowed arteries to the heart, which can become fatal if untreated. Waiting lists for treatment at the nearest heart hospital are two years long, even for the few families who can afford surgery. Most have no choice but to watch their children weaken and die.
Every time Khan comes home to visit his parents, queues form outside the house to seek his help. Poor people with desperately ill children walk for miles to Jhelum.
'They ring my mother to find out when I am coming home - then they line up outside the house,' says Khan. He recalls the case of one nine-year-old boy with narrowing arteries who came to see him with his father two years ago.
'I said to his father, 'I can't believe he has got to this stage and you haven't taken him to hospital,'' says Khan. 'He told me he had taken him to hospital but it was going to cost 250,000 rupees (HK$21,000) for an operation and there was no way he could afford it. So he just left it, knowing the boy was going to die soon.
'He was such a happy kid. He was still running about and he had no idea what was going on. I felt helpless. All I had was a stethoscope. I couldn't even give him the money for the surgery because it was too late for him to be operated on. He wouldn't have survived the operation.'
Khan takes out his phone and calls a friend in Jhelum, to find out if the boy is still alive. An hour later, a call comes back with the news that first the boy and then his devastated father passed away.
Abdul Razzaq Hospital will be home to the first charitable cardiology unit in Pakistan. Khan is setting up the hospital with fellow cardiologist Dr Azhar Kayani, director of medicine for the Pakistan Armed Forces and the Pakistani president's personal physician.
Kayani, who grew up in Badlote and studied at the same medical college as Khan in Lahore, says the hospital will cost the equivalent of HK$12 million and should open before the end of the year. The hospital is named after his father, a school teacher in Badlote, and Kayani has funded all the work so far.
Volunteers from the Essex hospital where Khan works are fund-raising for the heart unit and will help train the doctors and nurses. They have also helped find donated equipment from British hospitals.
One of the techniques Khan will bring to Pakistan is his ability to do mitral valve-repair surgery. He demonstrates the technique on a 14-year-old girl from a poor part of northern Pakistan in an operation that is broadcast live to an audience of cardiologists as part of a conference in Rawalpindi, near the capital, Islamabad. Repairing the heart vessel rather than replacing it with a metal valve means the teenager will be able to one day have children. When a metal valve is used, the patient must take blood-thinning drugs for life, and they make it hard for female patients to conceive.
Khan says of his work with children such as the 14-year-old: 'You never see them afterwards but you picture them in your mind, and you know that in a few years' time, she will hopefully be happy and married with kids.'
As he prepares for a new life in Pakistan, Khan is leaving behind a fresh wave of interest in Diana in Britain, with the 15th anniversary of her death looming and the movie Diana, starring Naomi Watts as the princess and chronicling the romance, in the pipeline.
Although he has been approached by the scriptwriters, Khan, who is being portrayed by Naveen Andrews (who played Sayid Jarrah in the television series Lost), has declined an invitation to co-operate on the film, maintaining his insistence since Diana's death that he will not divulge details of their private lives. He makes no secret of the fact, however, that he is angered by the continual focus on Diana's relationships and attempts in some quarters to suggest ulterior motives for her involvement in the good causes she championed.
'When people write about someone like Nelson Mandela, for instance, they keep details of his personal, private relationships to a minimum,' he says. 'Instead, they look at the good work he has done.
'There are so many other aspects to her, good and bad - like me. Everyone is like that. She did good things because she wanted to, not because of her status. She had an inner desire. It genuinely came from within her. You could tell. She didn't want anything back.
'I don't believe she ever did things like the landmines campaign to get media attention for herself. She didn't need to. She would get attention anywhere. All she had to do was wear a nice frock or get a new hairdo and she would get all the attention she wanted.
'It was the same with the patients and the hospitals she visited. She didn't need to go there to get attention.'
A book by Penny Junor - an author sympathetic to Prince Charles - has just been published. In it, Junor claims Diana was mentally unstable and that Charles stopped seeing his long-term mistress, Camilla Parker-Bowles, until his marriage had broken down irrevocably.
Khan describes this as 'rewriting history'. He says: 'There is no way at all that Diana was mentally unstable. There is nothing wrong with expecting your husband to be faithful and being angry when he isn't.
'Diana had every reason to believe that Charles and Camilla never stopped seeing each other. There was no doubt about it in her mind at all.'
He reveals details of one encounter between the princess and Camilla Parker-Bowles shortly before the royal engagement was announced, which, he says, Diana told him of on a number of occasions: 'Camilla came up to her and said, 'Charles is going to propose to you.' She told Diana before Charles proposed to her. Afterwards, Diana thought, 'Why did this woman know before me?' Obviously they were confiding.
'This is 100 per cent what Diana told me. She thought it was very odd. I would be very surprised if I was going to marry someone and my fiancee's ex-boyfriend came to me and said that.'
Khan says he stopped reading books and newspaper articles about Diana shortly after her death.
'I read a few things initially,' he says. 'Some were completely not true. Some were a third person speculating. I thought, 'A person has just died, for God's sake. Leave a little more time for people to get over the grieving and everything else.' I found it quite distressing so I just completely stopped reading anything.'
Now, as the mythology surrounding Diana continues to grow, Khan has claimed a place in the popular imagination as the love of her life and the man who - had she lived - could have saved her from her personal demons and made her truly happy by marrying her once her fling with Fayed had fizzled out.
Asked if he felt this to be a psychological burden, Khan replies: 'It is - of course it is. But at the time, we didn't know what was going to happen. We couldn't see the future.
'In retrospect, there are a hundred could-have-beens. She could be living very happily and married and having more kids, with me or with someone else. It could have led in that direction. I try not to think about these things. I can't change anything now.'
Ultimately, Khan lost a dear friend in tragic circumstances 15 years ago. It is plain to see that the pain of their unresolved parting lives on.
'Our last meeting was not at all happy,' he says, referring to the summer meeting in Kensington Palace where Diana told him their relationship was over. 'But that is all forgotten now. I think my mind has blanked a few things out.'
On the night she died, Khan tried to phone her, only to find she had changed her mobile number. 'I never had the chance to ask her about Dodi and find out what all of that was about,' he says.
So does he harbour any regrets? 'No - none whatsoever.' After a pause, however, he adds thoughtfully: 'The only thing is that it is different when you are with people, and when they are suddenly not around. All of a sudden, they disappear and you know you will never see them again. That is very difficult. Sometimes you think, 'I wish this' or, 'I wish that'. You would rather see them happy and alive, even if you are not together.'
Details of the charitable trust that will fund Dr Hasnat Khan's heart unit at the Abdul Razzaq Hospital in Badlote, Pakistan, are available at www.arwt.org .