Michael J. Fox and wife Tracy Pollan arrive at the 65th Primetime Emmy Awards in Los Angeles on September 22, 2013. Photo: Mario Anzuoni

London - Michael J. Fox was “stunned” to learn Robin Williams had Parkinson's Disease.

The 'Back to the Future' star - who was diagnosed with the condition in 1991 - hailed the late actor as a “true friend” and recalled all the work he did to raise money for his foundation, which raised money and awareness of Parkinson's, in a Twitter tribute.

Michael wrote: “Stunned to learn Robin had PD. Pretty sure his support for our Fdn (foundation) predated his diagnosis. A true friend; I wish him peace.”

Robin's wife, Susan Schneider, revealed on Thursday that the 'Hook' star was in the early stages of the disease when he took his own life.

Meanwhile, comedian Jeff Kilstein, 32, has spoken of how Robin - who battled alcohol addiction but got sober in 1982, relapsing briefly 20 years later - would help him whenever he was “struggling”

He told Us Weekly magazine: “Every time I struggled with addiction myself, or depression, or thought about quitting he would chat with me on the phone.

“I'd be sitting in my office and Robin Williams, in the softest voice, would just be helping me through it all. He would help me out of my darkest moments.”

And Jeff revealed his friend - who was found hanged on Monday following a long battle with depression - even paid his wages at one point when his radio show was struggling. - BANG Showbiz