Speaking at a memorial service for Michael Winner, Sir Michael Caine said he knew the director - who died in January this year - for 53 years.
The Italian Job actor said of meeting Winner the first time: "He was the kindest, nicest, most gentle person you could think of - and that is where I was completely wrong.
"He was the most miserable son-of-a-b**** once you got to know him, and I didn't understand why he did it.
"He was testing you, and he always tested people to see how far you would go before you disliked him.
"I said to him, 'Michael, you can go as far as you like with me. I will never dislike you. Do you understand that?'
"He said, 'Yes, I've got it'. And then he became my friend. And as many of you will not believe, he became a tender, gentle person with me all my life".
Cilla Black, Carol Vorderman and Sir Michael Parkinson were among the stars that honoured Michael Winner at a memorial service today.
A memorial service for the film director Michael Winner was attended today by two giants of British cinema - Sir Roger Moore and Sir Michael Caine.
The movie stars joined the veteran broadcaster Sir Michael Parkinson and Winner's wife Geraldine to pay tribute to the filmmaker-turned-food critic at the National Police Memorial in central London.
Winner, who set up the Police Memorial Trust following the death of Pc Yvonne Fletcher in 1984, was also hailed by Metropolitan Police Commissioner Sir Bernard Hogan-Howe, while a message from Prime Minister David Cameron was read out.
Around 100 people gathered in the north east corner of St James's Park to witness the unveiling of a plaque in honour of Winner.
Stars including Sir Michael Caine, Sir Michael Parkinson and Sir Roger Moore will speak later today at a memorial for film director and restaurant critic, Michael Winner, who died in January.
Winner's widow Geraldine Winner will also speak at the memorial along with Met Commissioner Sir Bernard Hogan-Howe.
Sir Michael Caine received a "personal" award on Saturday - the freedom of the borough where he grew up and made his acting debut.
The 79-year-old movie star collected the honour along with other luminaries from Southwark, south London, in a ceremony at St George's Cathedral, not far from Elephant and Castle, where he grew up.
Sir Michael said: "I've received awards before, but this is so personal, because it's about where I grew up."
Asked why he thought he had been given the award, he said: "I think it's because I come from here. I did my first acting in a youth club here, an amateur dramatic society. I'm part of what this place is."
The Alfie and Zulu star was nominated for the award by Peter John, leader of Southwark Council, who said: "Sir Michael has been an exceptional ambassador for the place where he grew up and an example for all Southwark residents."
The honorary freedom of the borough is given to individuals or organisations in recognition of their contribution made to life there.