John Bishop has begun his epic Sport Relief Challenge: Bishop's Week Of Hell, which will see him cycle, row and run from Paris to London in five days.
Setting off from the Eiffel Tower in Paris on Monday, Bishop is taking on the most physically gruelling test of his life as he completes a 290-mile triathlon.
Joined by Olympic gold medallist Chris Boardman, Bishop set off on his bike along the Champs Elysees at 0830 GMT, negotiating the cobbles around the Arc de Triomphe in Parisian rush hour traffic.
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As he pedalled off Bishop said: "'I am not sure how I'm feeling really right now - it feels a bit like I am in a Mission Impossible movie with the Eiffel Tower behind me. I just need to get my head down and get a few miles under my belt."
On day one Bishop will cover over 185 miles on his bike in less than 24 hours - the equivalent of 60,000 pedal strokes.
Then he will be joined by a team of celebrities as he spends the following day rowing across the channel from Calais to Dover, before embarking on three marathons in three days as he runs to London, finishing on Friday 2 March.
Speaking about the feat of endurance, Bishop's trainer Greg Whyte said: "The cycle alone is an extremely long distance to cover in less than 24 hours, even for an experienced ultra-endurance athlete. In addition to the fatigue in his legs, John will suffer in his hands, arms and neck from sustaining his cycling position for such a long time; not to mention his bum and groin!"
On day two as Bishop rows from France to England, he will be helped by celebrity rowers including Freddie Flintoff, Davina McCall and Denise Lewis, as he battles with seasickness.
The running stage of this epic triathlon will see Dermot O'Leary, Frank Skinner and Robbie Savage giving John some much-needed support, before finishing in Trafalgar Square in London.
All the ups and downs from 'John Bishop's Week of Hell' will be captured for a BBC documentary, to be broadcast in the build up to the Sport Relief Weekend, which is taking place from Friday 23 to Sunday 25 March.
Bishop hopes to raise enough money not only to pay for a vaccine against five deadly diseases for 250,000 children in Africa, but also to help people living incredibly tough lives in the UK.
You can get behind John by sponsoring him. For more information or to go the extra mile for Sport Relief 2012 yourself, you can enter the Sport Relief Mile today at bbc.co.uk/sportrelief