The duet, "(I'm Gonna) Love Me Again", was written expressly for the film, and the collaboration will be one of 22 songs on the album - but the only one to feature Elton's vocals. Taron performs all of the rock icon's beloved hits in the movie, and on the soundtrack.
"It was so important that the music I composed and recorded had to be sung by Taron," the "Candle in the Wind" singer said in a statement. "I left Taron in the hands of (producer) Giles Martin, who I trusted implicitly, because he's brilliant."
"I didn't want to be in Taron's shadows, watching over the process; I trusted them to do what they needed to do, artistically, and listening back I've been astonished with the results."
"I don't think any one actor has really done anything like this, ever," he added.
But the "Kingsman: The Secret Service" star admits capturing Elton's unique vocal talents was a big challenge on set and in the studio.
"I think there's moments in the film when I capture Elton a little more than others," he shared with the Beats 1 radio show World Record, "but there are moments where, because of where it sits in the film, it's more difficult to do that, because it's not naturalistic."
The soundtrack is set to be released on 16 May, while the film debuts at the Cannes Film Festival on 24 May.