SHE is the fierce MI6 boss known only by the codename M.

But now the true identity of James Bond’s mentor has finally been revealed — after a bit of sleuthing of which 007 himself would have been proud.

An eagle-eyed fan managed to freeze-frame a single camera shot in Skyfall lasting just a split-second and discovered that M’s real name is Olivia Mansfield. During the scene, Bond, played by Daniel Craig, is handed a box containing a Royal Doulton bulldog draped in a British flag, which is usually kept on M’s desk.

Zooming in on the box’s inscription, the words ‘From the Estate of Olivia Mansfield Bequeathed to James Bond’ are visible.

Since the revelation by blogger Phil Noble Jr, internet forums have been filled with speculation about the significance of the name.

One theory is that it is a tribute to Mansfield Smith-Cumming, the first head of MI6 who started the tradition of the organisation’s director signing letters with a single letter — in his case C.

Others have speculated it is a portmanteau of ‘man’s field’, alluding to the fact that M works in a male-dominated industry.

Meg Simmons, archive director for Bond production company Eon, said: “We’ve searched around and as far as we can see this is the first and only time anyone’s ever revealed M’s real name.

“It may not have been spoken, but if you were watching on a big enough screen it could have been visible, so we’d argue it’s now canon.”

Since Dame Judi Dench became the franchise’s first female spymaster in 1995, producers have dropped a series of hints about the character’s name.

In 2006’s Casino Royale, Craig’s 007 tells his boss: “I thought M was a randomly assigned letter. I had no idea it stood for?.?.?.’ To which she interjects: “Utter one more syllable and I’ll have you killed.”

And in Skyfall, Kincaid the groundskeeper refers to her as Emma, although many fans believe this is because he believes Bond to be calling her ‘Em’.