Robin Williams -- Private Celebrity Tribute Held

Robin William's famous friends and family gathered for a private memorial Saturday in San Francisco ... and Billy Crystal was in tears during the emotional tribute.

The event was reportedly held at the Curan Theatre and featured speeches from Billy, Whoopi Goldberg, Bobcat Goldthwait, Bonnie Hunt, Eric Idle, Williams’ three children and his wife, Susan.

Stevie Wonder handled the tribute's music ... and the event was attended by Bette Midler, Ben Stiller, George Lucas, Penny Marshall, Danny De Vito, Sarah Michelle Gellar, Jeff Bridges, Minnie Driver, Josh Groban, Seth Green, Eddie Izzard and Richard Lewis.

Robin's daughter Zelda Williams reportedly organized a majority of the memorial.