McLaren Mercedes’ 2010 Formula One driver’s line-up is finally set and as expected, a world champion joins Lewis Hamilton – a former champ himself – in the fold.

The twist is, however, it’s not the world champion we all first thought.

Jenson Button, the current F1 drivers champion has made his transfer to the Woking-based team, creating an all-British team with 2008 champ Lewis Hamilton. Button’s move to McLaren comes as a surprise to a lot of us, especially considering that Kimi Raikkonen was long rumoured to be the one teaming up with Hamilton at McLaren.

Nevertheless, the allure of pairing two world champs – and are compatriots, no less – on one team was good enough for McLaren to sign Button away from its new sister team Mercedes GP (formerly Brawn GP).

For the record, the last time two world champions raced for the same team happened 20 years ago (1989) when Alain Prost and Aryton Senna drove for McLaren.

Continued after the jump, photo courtesy of Brawn GP.

It remains to be seen how Button and Hamilton can co-exist together, especially when you consider the strain surrounding Hamilton’s relationship with his one-time teammate and fellow world champion, Fernando Alonso.

At the very least, Button can prove that his world title was not the result of a diffuser advantage, which he enjoyed for the most part of the 2009 season with Brawn GP. Now that the odds are fairly stacked, we’ll get to see what Jenson Button is really made of.

As for Raikkonen, it's now looking more and more likely that he will sit out the 2010 season after not being able to sign with any of the contenders. His agent, David Robertson, hinted that the Iceman would go ahead with his plan of giving the World Rally Championship (WRC) a shot.