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.
The funeral has taken place of film director Michael Winner, who died on Monday after a long battle with liver disease.
Sir Michael Parkinson and former Rolling Stone Bill Wyman were among the mourners who paid their final respects in north London.
A statement, issued by Michael Winner's office said if he had been alive to film it, he would have said: "Perfect, darling, perfect. A cold wind whipped a flurry of snowflakes across the cemetery - a film directors' dream."
Among the mourners were many of Michael's friends including Sir David Frost, Terry O'Neill, Don Black, Chris Rea and Henry Wyndham, chairman of Sotheby's.
Journalist and broadcaster Andrew Neil has paid tribute to Michael Winner, saying that he "didn't suffer fools gladly", but also didn't take himself too seriously.
Sunday Times restaurant critic AA Gill has paid tribute to his colleague Michael Winner, saying he was "immensely generous."
Gill said: "He had immensely loyal friends, and was very good in company.
"He was a natural as a restaurant critic, not because he knew a lot about food, but he did know about the business of hospitality, sitting around a table, telling stories.
"He was very good at what he did."
Andrew Lloyd Webber, who was among the close friends invited to Michael Winner's wedding, has paid tribute to him on Twitter.
TV mogul Simon Cowell has paid tribute to Michael Winner, saying that "laughter was never far away" when Winner was around.