Williams committed suicide on August 11, following a prolonged depression. He was 63.
The Oscar-winning actor and Crystal, 66, shared a long history as they co-hosted eight editions of TV show 'Comic Relief' and also worked together on 2006 event to raise money for Hurricane Katrina relief, said The Hollywood Reporter.
"He made us laugh hard, every time you saw him on television, movies, nightclubs, arenas, hospitals, homeless shelters, for our troops overseas and even in a dying girl's living room.
"Well, as genius as he was onstage, he was the greatest friend you could ever imagine: supportive, protective, loving. It's very hard to talk about him in the past because he was so present in all of our lives," Crystal added, sharing personal stories of Williams' ante-upping banter with the former's own immigrant relatives in private moments.
"For almost 40 years, he was the brightest star in the comedy galaxy," he said.