Sherlock star Benedict Cumberbatch has teased the upcoming series of the popular detective show.

The 38-year-old actor revealed that he knows the secret behind the reappearance of character Moriarty (Andrew Scott) in Sherlock.

Speaking to MTV (via Radio Times), Cumberbatch said it's a "very good idea".

He said: "I casually choose to forget in order to rediscover it again a little bit.

"But it's a very good idea, I do remember that detail. I'm just trying not to remember it so I don't blurt it out.

"I like casually forgetting, not least because there's a lot of other traffic between then and now but also because it's more fun because it's slightly more fresh."

Cumberbatch was at Comic-Con to promote his new movie The Penguins of Madagascar.