On his first day of testimony, Chan, 44, revealed for the first time how Chun, 33, died in her flat at Amoy Gardens in Kowloon Bay on October 6, 2011, seven months after they broke up when his then wife discovered the affair.

While admitting to killing Chun, Chan has pleaded not guilty to a count of murder.

The High Court heard that he visited Chun that night to break things off completely, because his wife told him she could try to forgive him if he did so. He testified that his wife was then on antidepressants after twice attempting suicide.

“I told [Chun] we could not continue our relationship because it could have a bearing on her, on me, and on my family, and my family had been hurt,” he said. “The sooner we’d stop it, the less we would be falling into a deep pit of despair.”

Chun’s reaction, he recalled, escalated from appearing dumbfounded to becoming “very ferocious”, and their fight turned physical after she slapped him twice.

When both of them lost balance and fell to the floor, Chan said he locked her arms across her chest and lay on top of her to weigh her down with his upper body.

“It happened quickly,” he said. “When she exerted stronger force, I did the same.”

It was when she stopped hitting him that he locked himself in the washroom to let her calm down, he said, only to find her not responding when he returned.

Hong Kong company director admitted killing mistress before murder trial, court hears

“I was very scared,” he said, his voice breaking. In court, Chan showed how he had put his finger to Chun’s nose to feel her breath, and imitated CPR on a stack of documents – which were transcripts of his telephone conversations with his wife – to show how he had attempted to rescue her, but to no avail.

“I thought by then she had lost her breath and died,” he said, burying his face in his hands as he cried. The court gave him a 10-minute break.

Chan, a self-identified Christian who graduated from the University of California, first met Chun in 2006, when he sought to expand his social connections and brought his friends and clients to Touch nightclub. Chun worked as a public relations hostess at the nightclub.

It was Chan’s first time visiting Touch and it turned into a regular activity, as he would go up to three times a month. Each time he would ask for Chun.

“I found her talkative, very lively, very happy,” Chan recalled. “She just knew how to make people happy.”

On one drunken night in 2008, he had sex with Chun for the first time and cheated on his wife, his high-school first love with whom he had two sons.

Chan and Chun started dating in mid-2008. He bought Chun a flat in 2009 and took out a life insurance policy with her listed as the beneficiary. But he broke up with her in March 2011 after his wife overheard one of their telephone conversations.

Finance director murdered mistress and sneaked away the body, prosecutors tell Hong Kong court

When Chun attempted to climb out of her window after the break-up, Chan recalled teasing her in a bid to calm her down: “If you just jump down from the flat like that, [the flat is] not going to be worth anything.”

“Nonsense,” he recalled her replying with a laugh.

Chan and his wife divorced last year because she said she could not accept the affair.

The trial continues with Chan’s testimony before Madam Justice Anthea Pang Po-kam.