United Kingdom, Dec. 1 -- Sir Elton John's producer found the legendary singer "extremely volatile".

The Rocketman hitmaker enlisted the services of Andrew Watt to work on Who Believes in Angels?, his album with Brandi Carlile, and the Grammy-winning producer has compared the 78-year-old musician to "Mozart or Beethoven" when he's working.

Andrew told People magazine: "[He's] a little more like Beethoven, I would say, and when he's writing, he's extremely volatile."

As a result, the 35-year-old producer tried to work with Elton in a particular way in order to stay out of his firing line.

He said: "My job is to read the room, and if you're in Elton's eye line as he's writing, you're in the f****** lion's den.

"So I would try and be ar...