World champion swimmer Alexander Dale Oen has died after having a cardiac arrest at an altitude training camp in the US.
The 26 year-old silver medallist at the 2008 Beijing Olympics was one of Norway's top medal hopes for London 2012 .
Dale Oen was found on the floor of his bathroom in Flagstaff, Arizona, by concerned teammates after collapsing on Monday evening, according to a statement by the Norwegian Swimming Federation.
Team doctor Ola Roensen began performing CPR until an ambulance arrived to take him to the Flagstaff Medical Centre, where he was pronounced dead.
Per Rune Eknes, president of the federation, said it was "the toughest day the sport of swimming in Norway has ever had."
Dale Oen won an emotional men's 100m breaststroke gold medal at the world championships in Shanghai last summer, just three days after the massacre in Norway by right-wing extremist Anders Behring Breivik that killed 77 people.
He dedicated his triumph to the victims of the attack, pointing to the Norwegian flag on his cap after the finish to send a message to his countrymen back home.
He said after the race: "We need to stay united. Everyone back home now is of course paralysed with what happened, but it was important for me to symbolise that even though I'm here in China, I'm able to feel the same emotions."
The Norwegian Swimming Federation said Dale Oen had played some golf and had a light training session on the day of his collapse.
Team coach Petter Lovberg told Norwegian news website 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."
Dale Oen is one of a number of young sportsmen to have suffered a cardiac arrest recently.
Bolton footballer Fabrice Muamba was released from hospital in mid-April weeks after collapsing during a match against Tottenham, and Livorno midfielder Piermario Morosini died after collapsing during a match against Pescara in April.