Just over a year ago, Elton John released 'The Union', a collaboration album with his idol, Leon Russell. Now, thanks to director Cameron Crowe, we get to see pretty much the entire canvas that story was painted on. Airing next month on HBO, 'Elton John / Leon Russell -- The Union' tells the story of how this particular union came to be, from Elton hearing an old Russell song that sparked fond memories up through the recording sessions and the renewed friendship that came out of the project.

"In the late 60's and early 70's, the one piano player and vocalist who influenced me more than anyone else was Leon Russell," Elton reveals in a clip from the documentary, "and it really p---es me off that everyone seems to have forgotten about him." This reignited love for his music, along with anger for a forgotten legacy, led Elton to contact producer T-Bone Burnett, who jumped at the the idea of producing the project. "It just rang, just seemed so right," says Burnett.

Once Elton convinced Russell that it was time to make another record, the wheels were fast in motion. With help from Burnett and Elton's wordsmith Benie Taupin, the four came up with, to paraphrase Todd Rundgren, an elpee's worth of tunes. The record also features guest contributions from Brian Wilson, Neil Young and others.

Directed by Crowe ('Almost Famous,' 'Jerry Maguire'), 'The Union' movie is a behind-the-scenes look at the evolution of the project -- from the planted seeds to the writing of the songs up through the recording process. We even get to see Elton in composing mode, something he has never allowed to be filmed before.

The documentary had its world premiere as the opening night selection at last year's Tribeca Film Festival, and will premiere Feb. 2 on HBO. “I’m a great fan of HBO and their extraordinary programming," Elton has said of the cable network. "I’m particularly thrilled that they will be airing 'The Union.'”

The collaboration of the two piano legends proved to be a huge success. It was Elton's highest-charting album in over 30 years, and Leon's best showing since 1972. The album garnered rave reviews and led to a sold out concert tour. Who knows -- ultimately, this giant snowball of love may have even helped spark Leon's induction into the Rock and Roll Hall Of Fame last year.

Watch a Making-Of Clip About Cameron Crowe's 'The Union':

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