The Welsh Team Sky rider triumphed after a 175.5 kilometre mountainous ride from Bourg-Saint-Maurice to Alpe d'Huez, which finished with a much-heralded final climb.

Dutch rider Steven Kruijswijk led for much of the 12th stage but the LottoNL-Jumbo man was reeled in before a five-man sprint finish.

Thomas, who also won stage 11 from Albertville to La Rosière yesterday, had enough in the tank to reach the line first in a time of 5 hours 18min 37sec.

This was two seconds clear of Dutch Team Sunweb rider Tom Dumoulin and three seconds in front of France's third place finisher Romain Bardet of La Mondiale and fourth placed Briton Chris Froome, who both received the same time.

Froome, the defending champion and Thomas' colleague at Team Sky, is hoping to win the race for a fourth time in a row and also holds the two other Grand Tours, the Vuelta a España and the Giro D'Italia.

However, it is now up for debate who Team Sky will ride for after the form of Thomas.

No British rider had won on the famous Alpe d'Huez before today.

"I am speechless," said Thomas.

"There wasn't a chance in hell I was going to win today.

"Can we just go to Paris now?"

An eventful stage also saw Italy's Vincenzo Nibali knocked from his bike as fans crowded by the roadside, denting the overall hopes of the Bahrain-Merida man who won the Tour de France in 2014.

He still recovered to finish seventh while Froome, who was cleared of an anti-doping violation on the eve of the race, also appeared to be shoved.

Thomas now sits on an overall time of 49:24.43 at the top of the general classification.

Froome is second, 1min 39sec behind, with Dumoulin third, 1:50 back.

The Tour continues with a flat 169.5km stage from Le Bourg-d'Oisans to Valence tomorrow.