Team Mitchelton-Scott's British cyclist Simon Yates won stage 12 of the Tour de France on Thursday, beating two other survivors of a mass breakaway in the Pyrenees.

Simon, the twin brother of his team captain Adam Yates, was the champion of the 2018 Vuelta a Espana, a multi-stage cycling race in Spain.

He also led the Italian race Giro d'Italia last year before a meltdown under pressure from eventual champion Chris Froome.

"I'm here to help Adam get the best result. He's doing well," he said of his twin who ranked seventh in the overall and is a potential Tour winner.

"But I'm really happy with this win. I got the green light to go from the team and timed it well.

"But now it's back to the day job," he smiled.

Simon was more than an hour adrift in the overall standings but punched the air in joy after outwitting his rivals to add this Tour de France stage to victories in Spain and Italy.

He came over the final climb with Bora-Hansgrohe's Gregor Muehlberger and Astana's Pello Bilbao but launched a long-range sprint for the line to win by a clear bike length.

Overall leader Alaphilippe led the peloton south from the pink-bricked city of Toulouse vowing to hold on to the yellow jersey but faced little pressure on the day.

He was ahead of the defending champion Geraint Thomas in the general ranking.

Third-placed Egan Bernal appeared to be the sweetheart of Colombia as increasing numbers of reporters from the South American nation arrived in anticipation of the 22-year-old pulling off something special.

"Time-trials aren't my thing," said the Ineos co-captain.

"I see Geraint taking some time off the other guys, but I'll lose a bit."

Mysterious quit in a bizarre way

In 116 years of racing at the Tour de France, riders have done all sorts of bizarre things, from jumping on trains to fighting with fans at mountain stops.

Rarely have they just vanished in the middle of a stage like Rohan Dennis did on Thursday during the first Pyrenean stage.

For a couple of hours on an otherwise uneventful day in the mountains, nobody was able to say where the time trial world champion had gone.

His Bahrain-Merida team even sent an alarming message out on social networks, saying all it cared about was "the welfare" of Dennis after Tour organizers announced he had pulled out of the race.

Dennis was spotted near the Bahrain-Merida team bus after the stage but did not make any comment about his decision to pull out.

"We are also confused," Bahrain-Merida team director Gorazd Stangelj said. "It was his decision today to stop at the feed zone. We tried to speak with him; he said 'I just don't want to talk,' and abandoned the race."

Stage 12 featured a 209.5-kilometer mountain range from Toulouse to Bagneres-de-Bigorre, France, on July 18.

Top 3 riders from stage 12

1. Simon Yates (UK/Team Mitchelton-Scott) 4 hours 57 minutes and 53 seconds

2. Pello Bilbao (Spain/Team Astana)

3. Gregor Muhlberger (Austria/Team BORA-Hansgrohe)

General ranking of Top 3 riders after stage 12

1. Julian Alaphilippe (France/Team Deceuninck-Quick-Step) 52 hours 26 minutes and 9 seconds

2. Geraint Thomas (UK/Team Ineos) +1 minute and 12 seconds

3. Egan Bernal (Colombia/Team Ineos) +1 minute and 16 seconds

(With input from agencies)