Singer Robbie Williams has been battling a mystery illness for the last four years.

The Take That star feared his depression had returned when he was feeling lethargic, but doctors later told him he was suffering from an unnamed condition.

Since being correctly diagnosed earlier this year, the singer has been receiving treatment to battle the illness, which he insists has "changed" his life.

He tells radio station Magic 105.4FM, "I thought I was lethargic and depressed as a person. I thought that was my make-up. I found out a few months ago that I'd been ill, completely by mistake, and I don't want to go into the whys and wherefores but what I had made you lethargic and made you depressed and I'd had it for years and not known and I'm on treatment for it. It's changed my life."

Here's the treatment he's on, the wxxker!

I love a lead balloon thread! 😆