Robin Williams doesn't know how John Travolta coped after his son died.

The actor - who stars in family movie 'Old Dogs' alongside John, whose 16-year-old son Jett passed away in January 2009 following a seizure while on holiday in the Bahamas - can't imagine there is anything "tougher" than outliving your children.

Referring to the Governors Ball, a party that took place after the Oscars ceremony in March, Williams said: "That's the worst thing that can happen to you, to have a child die before you. It doesn't get any tougher than that. There's such a kindness to him. Sitting there at the Governors Ball, to hang with him for a minute, that was the best moment for me."

The 'Good Will Hunting' star - who has three children, daughter Zelda, 20, and sons Zach, 26, and Cody, 18 - says his friend is like a "sweet panda" because he has dealt with Jett's passing with such dignity.

He added to the USA Today newspaper: "He's such a sweet man. He's the human equivalent of a panda. I saw him after the Academy Awards. It was good just to sit with him and say, 'How are you doing, man?' He said, 'I'm OK.' "

Williams, 58, also admitted the time off work he had last year following surgery to correct an irregular heartbeat had given him the opportunity to reassess his life. He said: "It's so nice having time off right now. There's no rush. Enjoy it. When you have something like heart surgery, you appreciate the simple things, like breathing. I'm taking it a lot easier."