He is known for his dislike of the press.
Speaking about the incident to Elle magazine, Knightley recalled: "When I saw him [Benedict] again, I said, 'Did you punch a journalist?' and he was like, 'I f***ing did.' Everybody needs a friend like that."
Film critic Mark Kermode has since tweeted to claim that he was the on the receiving end of the punch Knightley was talking about.
He told the Metro in 2009: "An actor very gently punched me on air for saying something about Keira Knightley. I called her Ikea Knightley as her acting was so wooden."
And she’ll most likely be awarded the same level of protection as the pair take to the promotional trail for their new film, the Alan Turing biopic The Imitation Game, out on 14 November, too.
Cumberbatch – heard earlier reading the 8am news from D-Day in 1944 on BBC Radio 4 – has enjoyed an interested relationship with the press over the years.
The many faces of Benedict Cumberbatch
The many faces of Benedict Cumberbatch
1/11 The many faces of Benedict Cumberbatch
The role that catapulted him to global fame: As a modern-day Sherlock Holmes in BBC drama Sherlock
2/11 The many faces of Benedict Cumberbatch
Benedict Cumberbatch stars alongside Keira Knightley in Alan Turing biopic The Imitation Game
3/11 The many faces of Benedict Cumberbatch
Cumberbatch bore an uncanny resemblance to Wikileaks founder Julian Assange in The Fifth Estate (2013)
4/11 The many faces of Benedict Cumberbatch
As Stephen Hawking in the 2004 BBC television film following the physicist's early years at Cambridge University
5/11 The many faces of Benedict Cumberbatch
Jonny Lee Miller as the Creature and Cumberbatch as Dr Frankenstein at the National Theatre in 2011
6/11 The many faces of Benedict Cumberbatch
Cumberbatch took on the role of tortured artist Vincent van Gogh in Alan Yentob's 2011 BBC drama-documentary Van Gogh: Painted With Words
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Benedict Cumberbatch as the idealistic Christopher Tietjens in 2012's Parade's End
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Looking sharp as John Harrison in Star Trek Into Darkness (2013)
9/11 The many faces of Benedict Cumberbatch
With Adelaide Clemens in BBC Edwardian period drama Parade's End
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Alongside Chiwetel Ejiofor in Steve McQueen's 12 Years A Slave, which won Best Film at the 2014 Oscars
11/11 The many faces of Benedict Cumberbatch
As confectionery millionaire and rapist Paul Marshall in Atonement (2007); Sherlock creator Steven Moffat said he wanted Cumberbatch for the detective series after watching the film
Most famously, he went through a freak spate of sign-holding in protest to photographers attempting to snap him on the set of Sherlock in 2013.
"Go photograph Egypt and show the world something important," one hand-written paper note, captured by the waiting pap, read.
As if suddenly realising that using the media is a great way to get messages out to the general public, he went on a sign rampage again, this time at an airport in a vain attempt to appeal to Prime Minister David Cameron.
His messily scrawled note read: "Questions we have a right to ask in a democracy."
This one was, however, a little too cryptic to have any deep and lasting impact on the hearts and minds of the general public, who weren’t sure quite what he was referring to.
Legend has it that he was commenting on the detention of David Miranda – the partner of the Guardian journalist who broke stories of mass surveillance by the US National Security Agency – at Heathrow Airport, though no one could confirm otherwise.
So he released a four-page hand-written message to explain himself.
"Hard drives smashed, journalists detained at airports… Democracy?" page one of four read.
"Prior restraint. Is this the erosion of civil liberties winning the war on terror…?" the second said.
The third was largely obscured by a man’s head, but was later confirmed to read: "What do they not want you to know? And how did they get to know it? Does the exposure of their techniques cause a threat to our security or does it just cause them embarrassment...?" No idea what happened to the fourth.
In a less cerebral moment, Cumberbatch was recently seen posing with paper napkin over his face as he attempted to eat lunch with Dakota Johnson undisturbed by the waiting paparazzi:
No, we’re not quite sure what the message there was either. But he obviously hates the attention. Which is why he did this at the Oscars: