Elite swimming coach Bud McAllister will leave Wales to take up a role in Australia.
The American has been based at the Wales National Pool in Swansea and has coached Team GB talents Jemma Lowe, Georgia Davies and Jazz Carlin.
"It was a very hard decision, it was by far the best job I've ever had," McAllister said.
"You don't get swimmers like Jazz Carlin very often, so it was very difficult to walk away from that."
McAllister added: "Ultimately the decision was a career move; I've always wanted to coach in Australia at a high-performance training centre."
Carlin, who McAllister has affectionately nicknamed 'Pitbull' for her will to win, missed out on a place at the London 2012 Olympics after illness wrecked her preparations.
But the 23-year-old bounced back to win three golds at the 2013 British Championships and she is expected to visit Australia regularly to continue her partnership with McAllister.
"Right now we're planning on her coming down and training with me as much as possible before the [2014 Glasgow] Commonwealth Games," McAllister added.
McAllister has previously guided United States superstar Janet Evans to four Olympics gold medals during her career and was twice voted American Swimming Coaches Association coach of the year.
The announcement of his departure comes a day after a deal was struck to to secure the future of elite-level swimming in Swansea.
Budget cuts following a poor London 2012 by Britain's swimmers meant that Swansea's status and funding as an Olympic and Paralympic training centre had been removed.
Swim Wales will instead fund the facility, helped by a direct investment from British Swimming into the sport's governing body in Wales.
But the good news appears to have come too late for McAllister to make any informed decision about continuing his role as head of the Intensive Training Centre in Swansea
"This job won't be available in September, I wasn't sure what was happening in September with the training centre here and no one could give me answers," McAllister said.
"This job [in Australia] is available now and it's a career move I've wanted to do, so I had to take the opportunity."