After the gory season finale of Sherlock's season 4 took the viewers by surprise, a new report claims that the lead detective duo in the series - Benedict Cumberbatch and Martin Freeman- might not return for season 5 due to their frosty friendship.

The English actors, who play Sherlock and his sidekick Dr John Watson, showcased a strained relationship on-screen during season 4 of the BBC series. But, according to The Sun, the actors are "hardly close" in real life and spend time apart in between shots.

Shedding light on the estrangement, a source told the newspaper: "Benedict and Martin aren't mates and they don't spend time together away from the show."

While the pair's close schedule might require them to work together for major part of the shoot, the report reveals that the long-time co-stars do not share the "warmth" anymore.

"They're professional and very polite to each other but there's not the warmth you'd expect after filming together for six years," said source adding, "There isn't a huge desire to come back for another season."

The popular sleuth series faces much criticism over the "gory" series finale that caused a divide between viewers. Sherlock season 4 episode 3 – The Final Problem – which closed the chapter for this year, also drew in the lowest-ever audience with only 5.9 million tuning in to watch the crime-drama.

The bleak future of the detective series has been hinted in the past by Sherlock co-creator Steven Moffat. The 55-year-old showrunner had said that the future of the show is dependent on the lead pair's hectic schedule and their willingness to return.

Even Cumberbatch spoke on the same lines before the season premiere, when he said that S04 has an end-game feel about it. In case you missed out the explosive season finale, click here to watch or visit PBS official website.