Sir Elton John was "not in good shape" while making 'Who Believes in Angels?'.

The 78-year-old music icon teamed up with Brandi Carlile to record their new album, but Elton has admitted to struggling with his health during the creative process.

The chart-topping star - who contracted a severe eye infection last year, which left him blind in his right eye and with "limited vision" in his left - said at a panel discussion in New York: "When you're in a studio and trying to come to grips with the fact that you want to make a great record, you can't always predict what's going to happen.

"We went in with no songs ... No plan. Just thought, 'This is the meeting of the minds and the talent. Let's get on with it.' But unfortunately, I was not in great shape. I was tired. I was exhausted."

Elton admitted that his health struggles led to "a lot of aggression and bad behavior" from him.

He shared: "More than anything I had so much doubt about my ability to come through in what we needed to come through. And that led to a lot of aggression and bad behavior.

"In a way, it was necessary for me to do that because I never had so much doubt and apprehension before I started the project."

Elton previously revealed that he's determined to remain optimistic, despite his health troubles.

The award-winning star confessed to feeling "miserable" at times. However, Elton also acknowledged that he's been very "lucky" in his life.

The singer - who has been married to David Furnish since 2014 - told the Guardian newspaper: "I'm an optimist permanently.

"I've got bad eyesight at the moment. There have been days where I've been miserable, but then I think about how lucky I am."

Elton remains hopeful that his eyesight will improve in the coming months and years.

The 'Rocket Man' hitmaker explained: "I've got a new respect for sight-impaired people and people who are totally blind, some of whom I'm in touch with. But to hell with it, I've got a great life, and hopefully my sight will improve."