He's solved numerous crimes with his best friend Sherlock Holmes over the years.

However, Dr John Watson is in for his most challenging role yet as he becomes a father in the upcoming 4th series of Sherlock.

Actor Martin Freeman, 44, was spotted carrying a decoy baby in a carrier as he filmed scenes with co-stars Benedict Cumberbatch and Amanda Abbington in London's iconic Borough Market on Tuesday.

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It's Daddy Watson! Martin Freeman was spotted filming scenes for the new series of Sherlock in London's Borough Market on Tuesday

Reunited: Martin was joined on location by co-star Benedict Cumberbatch, who returns to the role as detective Sherlock Holmes

Wearing jeans and a warm jacket, Watson certainly looked like a doting father as he kept his firstborn close to his chest.

It looks like Watson is going to be a hands on father to his baby daughter given the scenes, while his wife Mary (Amanda) was seen taking charge of a large hound.

The new baby will no doubt provide a new dynamic to the friendship between Sherlock and Watson, and the latter's marriage to former CIA agent Mary.

Never work with children or animals: Martin and Benedict were joined by co-star Amanda Abbington, who took charge of a rather large dog

In among the action: The cast and crew caused quite a stir as they filmed Sherlock during the busy lunchtime period at the market

Puppy love: The actors seemed quite taken with the lovable hound

As fans of the show will know, Mr Selfridge star Amanda, 42, is the real-life partner of Martin. The couple, who have been together for 16 years, have two children together, Joe, nine; and Grace, eight.

The new series comes two years after Series 3, which saw Mary revealing her pregnancy.

Sherlock co-creator Mark Gatiss gave a big hint this week that the new series will be inspired by Sir Arthur Conan Doyle's 1892 Sherlock story The Adventure of Silver Blaze.

Challenging: It looked like Benedict and Amanda were finding filming with the dog quite hilarious

The dog whisperer: Amanda attempts to reassure the dog as the trio prepare to shoot a scene

The new baby will no doubt provide a new dynamic to the friendship between Sherlock and Watson, and the latter's marriage to former CIA agent Mary

Amanda and Martin are real-life partners, having been together for 16 years and have two children together

The writer tweeted on Tuesday: 'The dog did nothing in the daytime… #Sherlock.'

The line is from Silver Blaze, one of the most popular Sherlock stories about the disappearance of a winning race horse and the murder of his trainer, John Straker.

Following the market scenes, the cast were later spotted half a mile away filming in Trinity Church Square in Borough.

From Cardiff to London: The scenes in Borough Market come after Benedict was spotted shooting on location in Wales on Monday

New mother: Series 3 of Sherlock saw Amanda's character Mary reveal her pregnancy

The scenes in Borough come after Benedict was spotted shooting on location in Cardiff on Monday.

Sherlock co-creators Steven Moffat and Gatiss confirmed the show was returning earlier this month following the New Year's special earlier this year.

In a statement earlier this month, Steven and Mark said: 'Sherlock series four - here we go again!

New plotline: Sherlock co-creator Mark Gatiss gave a big hint the new series will be inspired by Sir Arthur Conan Doyle's 1892 Sherlock story The Adventure of Silver Blaze

Silver Blaze is one of the most popular Sherlock stories about the disappearance of a winning race horse and the murder of his trainer, John Straker

Dapper: Benedict was back in his signature Sherlock look of long coat, gloves and a scarf

'Adventure, romance and terror': The series creators have promised lots of drama and intrigue in the new series

'Whatever else we do, wherever we all go, all roads lead back to Baker Street - and it always feels like coming home.

'Ghosts of the past are rising in the lives of Sherlock Holmes and John Watson bringing adventure, romance and terror in their wake.

'This is the story we've been telling from the beginning. A story about to reach its climax.'

Moving on: Following the market scenes, the cast were later spotted half a mile away filming in Trinity Church Square in Borough

On the hunt: Sherlock looks serious as he takes a call while taking charge of the hound

Action: Sherlock and Watson are back together following a two year absence since the last series - albeit a one-off New Year's special four months ago

'All roads lead back to Baker Street': The trio will be back in Marylebone in no time

Benedict, who performed at the live televised Shakespeare tribute in Stratford-upon-Avon on Saturday night, said he was 'thrilled' to be back as the detective.

He said: 'I can't wait for everyone to see season four. But you will have to wait... though not for long... And it will be worth it.'

Series four will return to BBC later this year with three feature length episodes.

Series four will return to BBC later this year with three feature length episodes

Ready for your close-up: A make-up artist tends to Benedict's face in between scenes

Bustle: Make-up and hair artists tend to the leading actors

Drawing a crowd: Dozens of market visitors stopped to watch the hit series being filmed