The event, titled An Experience with Mel Gibson, took place at Intercontinental London – The 02 on Saturday (13 November).
During the evening, Gibson told the crowd: “The man who directed all the Lethal films, Richard Donner, he was a big guy.
“He was developing the screenplay and he got pretty far along with it. And he said to me one day, ‘Listen kid, if I kick the bucket you will do it.’ And I said: ‘Shut up.’ “But he did indeed pass away.”
Donner died in July, aged 91. He had directed Gibson and co-star Danny Glover in all four Lethal Weapon films, from 1987 to 1998.
Gibson continued: “But he did ask me to do it and at the time I didn’t say anything. He said it to his wife and to the studio and the producer. So I will be directing the fifth one.”
The actor, who has directed filmsThe Passion of the Christ, Apocalypto and Hacksaw Ridge, didn’t reveal whether he would reprise the role of Martin Riggs, or if Glover would return as his cop partner Roger Murtaugh.
Gibson’s casting in a forthcoming John Wick prequel series was recently met with derision.
Fans were unhappy on account of the multiple allegations against the actor-director for making racist, anti-semitic and homophobic comments in the past.