Robert De Niro expressed his support for Billy Joel over his health diagnosis at the premiere of the singer's documentary on Wednesday.

Last month, the Piano Man singer cancelled his upcoming tour dates in the U.K. and U.S. after revealing that he had been diagnosed with a rare brain condition called normal pressure hydrocephalus (NPH).

He was also notably absent from the premiere of his forthcoming documentary, Billy Joel: And So It Goes, at the Tribeca Film Festival in New York on Wednesday.

During their opening speech at the event, Tribeca co-founders De Niro and Jane Rosenthal shared their support for the New York State of Mind singer.

"Billy wanted to be with us tonight, but as you may have heard, he's dealing with a health issue and had to postpone his performances - including this one tonight," Rosenthal said. "We know you'll join us in wishing him a speedy recovery."

De Niro then went on to praise Joel and the documentary.

"He's our piano man, a wonderful, beautiful part of the heart of our city," he gushed. "Tonight, you get to see the man behind the music and behind the legend. You're in for a real treat."

Directed by Susan Lacy and Jessica Levin, Billy Joel: And So It Goes is scheduled to air on HBO this summer.

The two-part documentary explores the personal struggles that fuelled Joel's songwriting and is set to include unseen performances, interviews, photos, and home movies.

During the premiere, Lacy assured the audience that the musician "will be back" soon, adding, "He said, 'Getting old sucks, but it's still preferable to getting cremated.'"