Arenbery Porte du Hainaut - Defending champion Chris Froome has said he was "devastated" after crashing out of the Tour de France on Wednesday following two falls twice on a wet and treacherous stage five.
"Devastated to have to withdraw from this years TDF. Injured wrist and tough conditions made controlling my bike near to impossible," he said on his Twitter feed.
"Thanks to the team & support staff for trying to get me through today. Wishing @richie_porte & @TeamSky the best for the rest of Tour!"
After the second crash, the 29-year-old was visibly injured and was seen shaking his head and holding his right arm before climbing into a Sky team car.
That signalled the end of his attempt to retain the yellow jersey he won in Paris last year.
Team manager Dave Brailsford said he had no updates on Froome's exact injuries but said it was all part of racing.
And he said attention will now turn to Richie Porte, who sits eighth overall at 1min 54sec from race leader Vincenzo Nibali following Wednesday's cobbled 152.5km stage from Ypres in Belgium to Arenberg Porte du Hainaut.
"I haven't heard from the doctor yet, Chris has gone back to the hotel and will fly home tonight," said Brailsford.
"Obviously it's devastating news for Chris and the team but we really knew it was going to be a tough race. We really believed in Chris and really thought he was going to win this race.
"It's not to be this year but in Richie Porte we've got a very capable guy who will now lead the team.
"I think like anything else, on a day like today when you have a setback, you've got to roll with it.
"It's part of sport, you've got to recalibrate your goals and go again. You might take a punch but you get up and go again.
"In Richie Porte, he's come into this team, we've selected him to be the number two, he had great ability today and great courage with Geraint (Thomas) to ride the cobbles the way he did and given the way it's timed at the minute, we've got an exciting couple of weeks to come."
The last time a reigning champion was forced to abandon the Tour was in 1980 when Frenchman Bernard Hinault quit due to a knee injury, although that wasn't from a crash.
In 1983, yellow jersey wearer Pascal Simon was forced out several days after a crash and he would never win the Grand Boucle.
Froome's withdrawal topped off a nightmare two days for the Kenyan-born rider, who also came off his bike on Tuesday's fourth stage.
Television pictures missed his two falls on a day in which numerous riders crashed even before the feared cobbled sections began.
After his first fall, Froome was seen with ripped jersey and shorts down his right hand side, trying to fix a mechanical problem by the side of the road.
Blood and grazing could also be seen on his hip through a rip in his shorts.
His Sky teammates quickly dropped back to pace him back up to the peloton.
Already he had begun the day with a splint to protect his left wrist that was injured in Tuesday's crash.
But the second time he went down, along with a teammate, Froome looked visibly distressed.
He stood by the side of the road holding his right arm across his body and making no attempt to get up and ride on.
When he started shaking his head, it was clear his race was over and he was soon bundled into the safety of a team car.
Vincenzo Nibali made the most of Froome's absence to take a firm grip of the yellow jersey, putting around two minutes into all his major rivals.
"I'm sorry for Chris, he fell yesterday and today, but that's also part of cycling," he said.
Incredibly, on a stage where the seven cobbled sections totalling 13km had been the major concern for riders, Froome actually crashed out before they even reached the first.