Billy Crystal's 54-year marriage to wife Janice is founded in "respect, humour, honesty".
The 'When Harry Met Sally ... ' star has been married to Janice since 1970 and they are parents to grown-up daughters Jennifer and Lindsay - and now the 76-year-old actor has revealed what it takes to sustain a healthy and happy relationship over five decades.
He told PEOPLE: "Respect, humour, honesty, and respect for our lives as individuals and as a couple. Just enjoy all the time that you have together. "Through the thin and the thinner."
The couple met as teenagers and became parents in their twenties while Crystal was starting out in his career as a stand-up comedian - and he says being a stay at home dad was a life-changing experience.
He said: "When I first became a dad back in [1973], Janice was working, and I was starting my career as a stand-up at night. So, during the day, I was ‘Mr. Mom’ and that changed my life totally."
"The responsibility as a 25 year old with an infant that can't get through the day without you. When you learn that you can love something much more than yourself, it was the greatest experience in my life as a person."
The Hollywood star went on to call his children the greatest achievement of his life, adding: "That's been my total effort of my life is to leave the world with two amazing daughters - grown women now, mothers of their own.
"And that they then teach their children/our four grandchildren what it means the responsibility in our world, which is changing constantly."
Billy previously revealed his four grandchildren used to love hearing him speak as his 'Monsters, Inc.' character, Mike Wazowski.
He told the Daily Telegraph newspaper: "For a while there, when I was on the phone to them they didn't really want to talk to me, they wanted to talk to Mike!
"They loved 'Monsters, Inc.' and then, when they caught up with 'The Princess Bride', I had to be Miracle Max."
