Sherlock fans have begun speculating that Martin Freeman's real-life partner will become Dr Watson's wife in the show, as the title of the second episode of the new series was revealed.
Benedict Cumberbatch and Martin were mobbed by fans and photographers while filming the hit BBC show in London, despite pleas from producers appealing to fans not to post spoiler pictures or give away locations.
Sherlock creators Mark Gatiss and Steven Moffat have revealed the title of the second instalment in the new series as The Sign Of Three. The title is a play on Sherlock Holmes author Arthur Conan Doyle's novel The Sign of Four, which sees Dr Watson meet Mary Morstan, who will become his wife.
It was recently revealed that Mr Selfridge star Amanda Abbington, Martin's real-life partner has joined the cast.
But asked if she plays Mary Morstan, Gatiss and Moffat simply repeated the official quote that Amanda's character "significantly impacts upon the lives of John and Sherlock".
Meanwhile, Benedict, who plays Sherlock, and Martin, who plays Dr Watson, were mobbed while filming outside Speedy's sandwich bar in Euston, which is opposite the door doubling for 221B Baker Street in the BBC show.
Benedict was wearing Sherlock Holmes' signature deerstalker hat for the shoot, despite his character taking a dislike to the headgear in the last series.
The eccentric detective flinched when, in the last episode of series 2, he was presented with a deerstalker by DI Lestrade and his Scotland Yard colleagues as a thank you present for helping solve a case. But it appears to have grown on him.