Norwegian swimming world champion Alexander Dale Oen has died of a cardiac arrest in Arizona at the age of 26, the Norwegian Olympic Committee said on Tuesday.
Dale Oen, who took an emotional men's 100 metres breaststroke gold medal at last year's world championships in Shanghai, had been attending an altitude training camp.
A silver medallist at the 2008 Beijing Olympics, he was one of Norway's leading medal hopes for the London Games starting on July 27.
"He died suddenly, without warning on Monday evening local time while with the swimming team in Flagstaff, USA," the Olympic Committee and Norwegian Swimming Federation said in a statement.
State broadcaster NRK said the swimmer's body had been found by a team-mate lying collapsed in a shower room.
Ola Ronsen, doctor to Norway's elite Olympians, was quickly on the scene and an ambulance arrived shortly afterwards but Dale Oen was pronounced dead at 2100 local time.
"My thoughts go first and foremost to his family in Oygarden," Per Rune Eknes, president of the Norwegian Swimming Federation said in a statement.
"This is the toughest day the sport of swimming in Norway has ever had."
Dale Oen won his world title last year in the immediate aftermath of the massacre of 77 people by far right fanatic Anders Behring Breivik in central Oslo and on the island of Utoeya.
He had struggled with his emotions after attacks that sent Norway into national mourning, touching the Norwegian flag on his swimming cap every time he entered the pool deck.
Photograph: Christinne Muschi/Reuters