Leon Russell recently spoke with Rolling Stone magazine about working with Elton.
He said that his Rock and Roll Hall of Fame induction could be credited in large part to his Union collaborator.
The musician also mentioned they plan another album together. Elton hopes to do a selection of rock standards in which he'd sing and Leon would play keyboards.
Meanwhile, the world premiere of Cameron Crowe's documentary, illustrating the creative process behind The Union, takes place on April 20 at the Tribeca Film Festival.
Although the event, to also feature a performance from Elton, is free, a special TFF wristband will be required.
There's a two wristband limit per person, and further details are expected soon.