Holmes doesn't look thrilled at the idea of becoming a sort-of uncle according to new pictures released ahead of the broadcast of 'Sherlock' season 4, but with Watson becoming quite the hands of father he's definitely going to have to get used to it.

Benedict Cumberbatch and Martin FreemanBenedict Cumberbatch and Martin Freeman in 'Sherlock' season 4

The fourth series of 'Sherlock' will return with episode one 'The Six Thatchers' on New Year's Day, seeing the return of Benedict Cumberbatch and Martin Freeman as Holmes and Watson, as well as Amanda Abbington as Mrs. Watson, Mark Gatiss as Sherlock's nemesis brother Mycroft and Una Stubbs as the ever-loveable landlord of 221b Baker Street Mrs. Hudson.

Amanda Abbington, Benedict Cumberbatch and Martin FreemanAmanda Abbington, Benedict Cumberbatch and Martin Freeman in 'Sherlock' season 4

Plus, there's a brand new character on board; the villainous Culverton Smith whom we first glimpsed in the teaser trailer. 'He's the darkest villain we've had', creator Steven Moffatt said recently. 'There was always something charming and engaging about Moriarty. There was something fascinating and actually amoral, rather than immoral, about Charles Augustus Magnussen. This guy is the purest evil.'

Toby JonesToby Jones in 'Sherlock' season 4

There's also baby Watson - though we can't imagine that she (or he) has many lines in the series. Though we'd be very much surprised if Sherlock didn't try his very best to teach she or he his own name. In one of the three episodes of the new series we are likely to see a christening, judging by an image of Mrs. Hudson that has surfaced in which she's dressed in her smartest attire while Sherlock stands beside her with his head bowed in front of an object that looks very much like a baptismal font. 

Una StubbsUna Stubbs in 'Sherlock' season 4

Currently, there are no full details on any other new characters in the show, though the names Thatcher and Sherrinford (the latter being Sherlock and Mycroft's legendary elder brother, who has been referred to in earlier episodes, though not by name) have of course been teased previously.

More: Watch the trailer for 'Sherlock' season 4

'Sherlock' season 4 will begin airing on BBC One on January 1st 2017.

Benedict Cumberbatch and Mark GatissBenedict Cumberbatch and Mark Gatiss in 'Sherlock' season 4