Benedict Cumberbatch accidentally told Stephen Hawking about a secret movie role when they were "knee-deep in margaritas".

Sophie Hunter and Benedict Cumberbatch

Sophie Hunter and Benedict Cumberbatch

The 40-year-old actor recalled how he confessed to the Professor that he would be taking on the role of Khan in 2013's 'Star Trek Into Darkness' despite his casting being kept a big secret.

Speaking on BBC's The Graham Norton Show, he shared: "It is the most extraordinary experience. We were at the Royal Society for a discussion on the future of science and it was a long night, so we decided to go for a drink.

"We got knee-deep in margaritas and it was at that drunken moment I thought I would tell him I was playing Khan in Star Trek. Stephen was the only person I told. He liked the fact I had told him. It made him smile."

Meanwhile, the father-of-one - who has 16-month-old son Christopher with his wife Sophie Hunter - is currently on a world promotional tour for his new movie 'Doctor Strange' and he previously revealed he had to "step out of his comfort zone" for the role.

He said: "People ask me what I have in common with my character and I feel that's really it. I was having to do action hero stuff on a level I've never done before and wire work and kung-fu moves and casting these spells.

"Amazing movements like tutting with the fingers and all these delicate hand movements as well as body posturing. I was learning that as much as my character was, so both of us were stepping out of our comfort zone so that's something I could draw on for the characterisation."