The 20-year-old has signed five-and-a-half-year contract at Stamford Bridge, but will be loaned back to the Belgian side for the rest of the season.

He told the club website: “To come to a team like Chelsea is a dream but now I have to work hard to achieve the level that’s necessary.”

Meanwhile, Blues striker Philipp Prosenik, 18, has joined AC Milan.

The Austrian has moved to the San Siro for an undisclosed fee.

Chelsea manager Andre Villas-Boas had insisted the arrival of De Bruyne was nothing to do with him and that it was down to “club policy for the future”.

He explained: “It’s a target that’s decided by the club, that I knew about for quite some time.

“In the sense that it’s the club policy for the future, it’s the right thing [to buy him] and I’ll do everything in my power for him to reach maximum potential.

“But it’s down to the club in decision-making. I’m a manager who respects club policy.

“A club has to look to the future, whether it’s with this manager or another. He’s a good bet for the future.”

De Bruyne scored five goals last season as Genk were crowned Belgian champions for the third time.

He has played twice against Chelsea this season, appearing for Genk in the 5-0 Champions League group stage defeat at Stamford Bridge and again in the 1-1 draw at the Cristal Arena.

De Bruyne added: “I have signed now and I will go back for six months on loan to play some games and gain more experience.

“Next season it would be normal to be loaned out, but I will start the preparations here at Cobham, and if it goes really well maybe I will stay but probably it will be a team a little level less than Chelsea but bigger than Genk.”