Tributes have started to pour in for world 100 metres breaststroke champion Alexander Dale Oen who has died aged 26.
The Norwegian was at a training camp in Flagstaff, Arizona, where he was reported to have suffered a cardiac arrest.
Per Rune Eknes, the president of the Norwegian Swimming Federation, told www.vg.no: "This is just awful, especially for the family and close friends, and also the sport of swimming."
Norwegian media report Dale Oen, the Olympic silver medallist, was found on a bathroom floor at 9pm local time yesterday.
He was taken by ambulance to the medical center where, despite repeated attempts at resuscitation, he was pronounced dead.
Dale Oen's death comes little more than a week after the death of Italian footballer Piermario Morosini following a heart attack during a game.
That in turn followed Fabrice Muamba's cardiac arrest while playing for Bolton at White Hart Lane although he survived and has now left hospital.
The Norwegian team coach Petter Lovberg told www.vg.no: "We are all in shock, this is an out-of-body experience for the whole team over here.
"Our thoughts go out to his family who have lost Alexander too early.
"Words cannot describe the grief they must feel.
"For us here in Flagstaff it is important now that we stand together and take care of each other.
"It is an unreal situation and we have some tough days ahead."
World governing body FINA released a statement which read: "FINA was shocked to learn about the sudden death of prestigious swimmer Alexander Dale Oen at the age of 26 in a training camp in Flagstaff (Arizona, USA), on April 30, 2012.
"Dale Oen has been one of the most promising revelations at the 2008 Olympic Games, winning a silver medal in the 100m breaststroke, an event in which he obtained the victory (the first ever for his country) at the 2011 FINA World Championships in Shanghai (CHN).
"He was therefore one of the most talented swimmers in this stroke and was certainly preparing a brilliant participation at the upcoming Olympic Games in London.
"In everyone's memory is also present his courage in Shanghai when shining in the pool immediately after the sad events that had taken place in Norway.
"He had given to media and fans an image of a brave and sincere athlete, paying a heartfelt tribute to his compatriots from the pool deck in China. His example had been one of the most vivid moments of those Championships.
"FINA shares the mourning of the entire Norwegian swimming community and addresses its most sincere condolences to his family and friends."
Quadruple Olympic breaststroke champion Kosuke Kitajima, who is looking to become the first man to twice successfully defend a swimming title in London, Tweeted: "In shock over the passing of a dear friend and great rival. RIP Alex."
South African Cameron van der Burgh, double bronze medallist in Shanghai, added: "To my greatest rival. My greatest friend. My brother in breaststroke. May you rest in peace. One love."
European governing body LEN bureau member and British Swimming chief executive David Sparkes told Press Association Sport: "I think he was an outstanding athlete and a great inspiration - not only to everyone in swimming but in particular to swimmers in Norway.
"He was just outstanding and he very much did it his way.
"He clearly had a great future potential as being Olympic champion in London - he was a class of his own.
"It is a great loss, it is hard to believe he is no longer with us.
"He was a charming young man and so gracious in victory.
"It was so nice to see someone from a country not famed for its swimmers but more for its skiers doing so well."
Sparkes added: "Swimming is one of those strange sports where they are rivals but also great friends. Often they train together and compete together. It will have affected a lot of people in the sport."
Dennis Pursley, British Swimming head coach said: "The international swimming family is small and tightly bonded, so it is always difficult when we lose one of our own."