He said it is something he and wife Blake Lively will 'always be deeply and unreservedly sorry for'.
Ms Heard has alleged that Mr Depp had nicknames for all of her male co-stars that he considered a 'sexual threat'.
The Hollywood actor is giving his fourth day of evidence in his libel action against The Sun newspaper.
Mr Depp said he used the word 'headbutt' because that was the word Ms Heard used.
The British actor was speaking at a demonstration in Hyde Park.
The actor is suing over an article that referred to him as a 'wife-beater'.
The British actor said he had a lukewarm attitude towards tying the knot.
The actress was crowned Woman Of The Year at the GQ Men Of The Year Awards in Berlin.