Sing us a song, piano man. 

The new documentary “Billy Joel: And So It Goes” covers the life and career of the legendary musician, 76, featuring interviews with Joel, family members, his ex-wife Christie Brinkley, and fellow industry heavyweights such as Bruce Springsteen and Paul McCartney. 

“I asked [Joel] … at the very beginning – if there were any sensitive areas. Not that I would have necessarily stayed away from them, but I wanted to know what they were,” co-director Susan Lacy exclusively told The Post. “And his answer to that was, ‘tell the truth. That’s the only way to go.”

She explained that while probing into the “Vienna” singer’s life, “nothing was off limits.” 

“He didn’t see the film until it was finished, so he stuck by that,” Lacy explained. “And we took that as permission to tell the real story about Billy Joel.”

In fact, the “Uptown Girl” crooner had no editorial control over the film. 

“I think it was courageous of him to give us that carte blanche and trust in us to tell that story – because not everybody would do that,” co-director Jessica Levin told The Post. “I think he realized, ‘I need to do my part, and try to go places where it might not be 100 comfortable for me.’” 

The film covers topics such as Joel’s suicide attempt in his twenties, after he had an affair with his friend’s wife – Elizabeth Weber, who would become Joel’s first wife from 1973 to 1982. 

Joel then went on to marry Brinkley, 71, from 1985 to 1994, with whom he shares daughter Alexa Ray Joel, 39; Katie Lee from 2004 to 2009, and he tied the knot with his current wife, Alexis Roderick, in 2015. The two share daughters Della Rose, 9, and Remy Anne, 7. 

In the documentary, Joel sounds matter of fact about his attempt to take his own life. 

“It was a long time ago. He was young, and he was heartbroken. He felt quite lost at that point,” Lacy said. “There were a lot of emotional elements going on. He just didn’t know which way to turn.”

Levin chimed in: “I think it’s important that it’s not that he doesn’t take suicide and depression seriously. He certainly takes those topics seriously. But for him, it was a very early moment in his career….Honestly, Billy is kind of a matter of fact guy and he’s a guy that does try to build and move on.”

After he saw the finished documentary, Joel wrote Lacy a note. 

“He thanked me for so masterfully connecting the dots of his life and said  that he now knew why he did what he did.”

“There’s a real dichotomy with Billy – a man who put his life out there in his lyrics, but he doesn’t believe in self-examination particularly….He put it in his music. And that saved his life,” she went on. “He used music to cope with his life and to express his life and to what was going on. But I don’t think he ever stood back and went, ‘let’s see how these dots connect with each other.’ And that’s what we did in this film.” 

In May, Joel revealed that he’s been diagnosed with normal pressure hydrocephalus, a disorder that happens when cerebrospinal fluid (CSF) builds up inside the skull and presses on the brain, disrupting cognitive functioning.

Amid his health battle, he skipped the June premiere of “Billy Joel: And So It Goes” at Tribeca Film Festival. 

Lacy said his health issues didn’t impact the project because it happened after they finished filming. 

“I think he’s working on recovering, and he’s resilient. He’s a fighter.” 

Aside from being a nod to one of his songs, the doc title “And So It Goes” encapsulates Joel’s approach to life. 

“Which is, and, so it goes. ‘I’m going to move on [from setbacks] and I’m not finished yet.’ And here he is today, with this incredibly strong woman as his wife and these beautiful daughters,” Levin told The Post. “It’s important to him to stay around as long as he can for his children and his family. He cares deeply about that. He is the ultimate romantic.”

“Billy Joel: And So It Goes” Part One premieres on HBO Max on Friday, July 18 at 8 p.m. ET, followed by Part Two on Friday, July 25.