The International Olympic Committee has released a statement expressing its sadness after two French Olympians died while filming a reality TV survival show.
Yachtswoman Florence Arthaud, 57, and the two Argentine pilots also perished in the accident, which is yet to be explained.
A statement from the IOC read: "We are shocked by this sad news. Our thoughts are with the families and friends of these great athletes who have left us.
"With them, the world of sport and the Olympic family have lost three of their key members. They were all not only champions in their sport but also contributed greatly as role models.
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"The Olympic movement mourns with their families and friends, their fellow athletes, the French National Olympic Committee and with France. The Olympic flag will be flown at half-mast for three days at the IOC Headquarters to honour these great champions."
Muffat won three medals in her career, including Olympic gold in the 400m freestyle at London 2012, while Vastine clinched boxing bronze at the Beijing Games seven years ago.