(CNN) -- Norway's world 100-meter breaststroke champion and Olympic silver medalist Alexander Dale Oen has died suddenly at the age 26.
In a statement on its official website, the Norwegian swimming federation said Dale Oen was found collapsed in his bathroom after a cardiac arrest late Monday in Arizona where he was participating in a training camp.
The team's doctor Ola Roensen tried to resuscitate him before he was taken to the nearby Flagstaff Medical Center. He was pronounced dead at 9 p.m. local time.
"We're all in shock," Norway's national swimming coach Petter Loevberg said. "This is an out-of-body experience for the whole team over here. Our thoughts primarily go to his family who have lost Alexander way too early."
Dale Oen won the 100-meter breaststroke at last year's world championships in Shanghai, three days after Anders Behring Breivik killed 77 people in a bomb and gun attack in Norway.
The swimmer poignantly pointed to the Norwegian flag on his cap, and later dedicated his win to the victims.
"Everyone back home now is of course paralyzed with what happened," he said after the race. "But it was important for me to symbolize that even though I'm here in China, I'm able to feel the same emotions."
Dale Oen also won silver at the 2008 Olympics in Beijing for Norway's first ever swimming medal and was expected to be one of the country's main hopes for gold in London later this year.
World swimming's governing body FINA said he was "certainly preparing a brilliant participation at the upcoming Olympic Games in London."
Norway's swimming federation did not give a cause of the cardiac arrest. It said Dale Oen had only had a light workout on Monday and had seemed in good health.
"This is the blackest day in the history of Norwegian swimming," said Per Rune Eknes, president of the federation.
Four-time Olympic breaststroke champion Kosuke Kitajima, who Dale Oen would have been looking to beat in London, tweeted that he was "in shock over the passing of a dear friend and great rival. RIP Alex."
Cameron van der Burgh of South Africa, who took bronze behind Dale Oen in Shanghai last year, wrote on Twitter: "To my greatest rival. My greatest friend. My brother in breaststroke. May you rest in peace. One love."
In his final tweet written on the day of his death, Dale Oen wrote that he was looking forward to returning to his hometown, Bergen.
"2 days left of our camp up here in Flagstaff,then its back to the most beautiful city in Norway."
Dale Oen's death comes 18 months after American open-water swimmer Fran Crippen died during a race in the United Arab Emirates, also at the age of 26.
Crippen's death was caused by heat exhaustion leading to drowning.