It might not have been the world's best kept secret, but Sir Ian McKellen has announced that he will reprise his role as Gandalf The Grey in the forthcoming two-part adaptation of The Hobbit.

The Lord of The Rings prequels will be helmed by Guillermo Del Toro, and McKellen said that the Pan's Labyrinth director's offer was one he jumped at.

"I spoke to Guillermo in the very room that Peter Jackson offered me the part," Sir Ian told Empire.com. "Obviously it's not a part that you turn down, I loved playing Gandalf.

"Guillermo will be getting round to starting the script in about six weeks when he's finished filming Hellboy 2."

And on the burning question of what the films and the plot will look like in the Mexican's hands, the revered actor said he was as clueless as the rest of us.

"Well I've read The Hobbit so I’ve got a good idea of what the story would be,” he said. “But as to how it’s going to work over two films and what going to happen on screen, well Guillermo has not got down to working out the major details yet – I can tell you it’s going to be amazing though.”