According to Le Dauphine, the alert was given at about 7:15am, reporting a fall at the Great Bosse, in the Bosses ridge, on the normal route to the top of the summit.
The Chamonix PGHM launched an aerial search operation with two gendarms and a SMUR doctor on board the civil protection helicopter.
The body of the young man was discovered on the Grand Plateau, under the northern slope of the Bosses ridge (3,817m). Every effort was made to save the victim, but sadly it was unsuccessful, the men didn't survive.
The young man was not properly equipped
Lieutenant Colonel Stéphane Bozon, commander of PGHM in Chamonix, explained that «the man fell around 300 metres and lost his sports shoes, not equipped with crampons". "Also he didn't wear a helmet or a harness." he added.
The trail runner departed the evening before, from the village of Les Houches, near Chamonix, with a friend, also trail runner, for the ascent of the Mont Blanc massif during the night. He was accompanied by his friend until the Tete Rousse Hut (3,167m), then he continued the ascent alone, reaching the Mont Blanc summit at about 6am.
The accident occurred when the man was descending the massif on the Bosses Ridge, the man fall at the first bosse "hump", a "dangerous one", said Jean-Louis Verdier, assistant of mountain safety in Chamonix.
Bosses ridge: the first bossse "hump" is quite steep (35°) and crevassed.
According to the analysis of Stéphane Bozon, at the level of the Great Bosse, on a narrow piste, he passed some mountaineers and displaced himself to let them pass, when he was caught "into a very big fall with strong kinetics". "The snow is hard and icy outside the pistes, there is no ability to hold in a fall", he added.