Actor Laurence Fox has apologised for swearing at a heckler while performing in a play.
Fox said the audience member at London's Park Theatre had become "so loud and so impossible to deal with" that he could not continue without reacting.
The star of ITV's Lewis is playing French statesman Charles de Gaulle in The Patriotic Traitor, written and directed by Yes Minister's Jonathan Lynn.
According to the Evening Standard, during the live performance on Tuesday evening Fox scolded a man in the front row with the words: "I won't bother telling you the story because this c*** in the front row has ruined it for everybody."
He left the stage and did not return for the final bow.
Speaking on the BBC Radio 4 Today programme, Fox said: "Can I just start by apologising to the other 199 people in the theatre for my use of language.
"It was a very emotional part of the play and I was very upset about it, and then upset about how I'd behaved."
He explained: "This gentleman in the theatre started heckling, muttering and heckling early on during the play, and then towards the end started telling me to eff off ...
"And it became so loud and so impossible to deal with, that I really should have had a little speech prepared and gone 'Excuse me sir, you can either leave' - or whatever."
He said he regretted using the swear word "in the heightened emotion of the thing".
The 37-year-old added: "It's not an interactive stand-up comedy show. And therefore, if someone is hell-bent on heckling, they are ruining it for everybody and particularly the rest of the audience and the actors. So I think it becomes an un-performable play."
A spokesman for the Finsbury Park venue said on Wednesday: "Park Theatre takes the welfare of its performers, staff and patrons very seriously.
"We are investigating the incident, and have no further comment at this time."
After the performance, BBC producer Lewis Vickers tweeted: "Exceptional performance of #PatrioticTraitor @ParkTheatre and @LozzaFox (Fox's Twitter handle) dealt brilliantly with that cunning stunt at the end."
Fox replied: "He was a cunning stunt wasn't he? Apologies for my being a cunning stunt as well ... So glad you liked it."
The Patriotic Traitor centres on the relationship between General de Gaulle and Philippe Petain, played by Tom Conti.
Formerly close friends, the two men ended up on opposite sides in the Second World War.
Fox is a member of the famous acting dynasty which includes his father James, best known for The Servant and Downton Abbey.
His uncle Edward starred in The Day Of The Jackal and also portrayed King Edward VIII in ITV's Edward & Mrs Simpson.
Fox's cousins Emilia and Freddie also act, and are known respectively for the BBC's Silent Witness and Channel 4's Cucumber.