HBO has released the first official trailer for the upcoming documentary "Robin Williams: Come Inside My Head."

A look at the life of the late and great comedian, the documentary delves into Robin Williams's private struggles. He battled depression for years before he tragically died by suicide in 2014. The trailer touches on this inner turmoil, making it as sad to watch as it is powerful.

Not only does the documentary use ample footage of Williams taken from interviews and standup shows, it includes insight from those who knew him well. The trailer shows clips, including interviews with fellow big-name comedians and one of his children.

"He was really comfortable on stage," Steve Martin says. "Off stage, I just really felt he was holding himself together.

Watch the moving trailer below.

"Robin Williams: Come Inside My Mind" is directed by Marina Zenovich. The documentary's release date has not yet been announced.