“I know some countries don’t like to invite foreign athletes to their facilities, but rivalry creates good training,” Zirk said. “The times for my 200 metres butterfly and Siobhan’s 200 metres freestyle are similar, so we race each other.”

He added: “She is very excited that I have a kid, and always wants to see pictures. I think it has given her a little spark. She is training really well, and looking good.”

Hiring a lane in Estonian capital Tallinn’s one Olympic-size pool cost Zirk €100 (HK$840) per hour. Training for 20 hours a week would burn through HK$16,800.

Sharing lanes with public trundlers, meanwhile, sapped Zirk’s motivation and had him questioning his swimming future.

Fifth in the 200m butterfly at February’s World Championships in Doha, the 24-year-old competed with Haughey for Energy Standard, the team who won the 2019 and 2021 International Swimming League.

The pair share a coach, Tom Rushton, whose HKSI camp also involves swimmers from Israel and India.

“Most of the pools in Estonia are privately owned, so their goal is to make a profit,” Zirk said. “There is more demand than supply, so they can create a bidding war.

“Our government could do more to support sports. We have no national centre … I cannot book a swimming lane in the evenings, because they are taken by clubs.

“The Olympic Committee is good, but their focus is funding, and they are happy if we go abroad for training camps. I pay around €1,000 for my flights to Hong Kong, then my food and accommodation are covered.”

Zirk claimed a host of Estonian records before turning 16, then sought greater competition by leaving home for the high-performance swimming programme at England’s Plymouth College, the alma mater of Olympic champion swimmer Ruta Meilutyte and diver Tom Daley.

“My parents aren’t super-wealthy, so it was a big challenge to fund me, but going to Plymouth was the best decision of my career,” Zirk said.

He competed in the Tokyo Olympics, with a best finish of 13th in the 200m freestyle, but his optimism about this summer’s Paris Games contrasts with the lows of 2023.

“I didn’t want to swim any more,” he said. “I would not go to practice, or I would swim 1km then get out of the pool. We usually cover 6km.”

Zirk partly attributes his renewed outlook to the birth of son Lukas late last year. Having performed well beneath his expectations at the previous worlds, Zirk went to the 2024 edition “not really rested, and after not much training”, when Lukas was three months old.

“From the first race, I was swimming the same speeds as the previous year,” he said.

His partner and son then joined him at a training camp in the United States.

“I was sceptical about having them with me,” Zirk said. “It turned out to be the best camp of my life. Playing with your kid, and seeing him smile, generates a chemical reaction.”

Zirk’s surge in form has made him more appealing to sponsors, won him extra funding in Estonia and brought television appearances – all of which Haughey can relate to as she carries Hong Kong’s hopes.

In the weeks preceding the Games, Zirk will base himself back in Tallinn.

“Maybe someone else will pay for me to use the pool,” he said. “The schools are off, so fewer kids will be swimming.”