Sir Michael Gambon, 74, has been battling short-term memory loss for several years.
"It’s a horrible thing to admit but I can’t do it"
However the Bafta-winning star has heartbreakingly been forced to admit defeat, after being forced to wear a prompt earpiece whilst reading for a West End play.
Sir Michael, who was admitted to hospital twice in 2009 after suffering severe panic attacks, said: “There was a girl in the wings and I had a plug in my ear so she could read me the lines.
"After about an hour I thought, ‘This can’t work’."
He added emotionally: "It’s a horrible thing to admit but I can’t do it. It breaks my heart.”
Sir Michael, who is currently appearing as Henry Tyson in Sky Atlantic's Fortitude, will now avoid stage roles.
But, as doctors have twice found him clear of Alzheimer’s following tests for the disease, the veteran actor is keen to continue his film and television career.