Sir Ian McKellen pulled out of writing his memoirs and handed back a reported £1 million ($2.07 million) advance because he found it too painful to delve into his past.
Appearing yesterday at the Oxford Literary Festival, Sir Ian said he had realised he wished to keep his private life separate from his public life.
Asked why he had cancelled the deal with Hodder & Stoughton, he said: "I put nine months aside to do it, and I got a very handsome advance. Then I sent the money back. It was a bit painful - I didn't want to go back into my life and imagine things that I hadn't understood so far.
"Frankly, if anybody wants to know anything about my public life, my working life, my career, it's all catalogued in greater detail on my website than could ever be put into a book. The privacy of my life I don't quite understand myself, and it has nothing to do with what I do for a living. So there you go - I'm sorry."
Sir Ian, 76, came out as gay in 1988. A co-founder of Stonewall, the gay-rights organisation, Sir Ian spoke out against people "who quote God" to attack homosexuality, even suggesting Jesus may have been gay.
He also attacked Ian McEwan over recent comments about transgender people. The author last week said: "Call me old-fashioned, but I tend to think of people with penises as men."
Sir Ian said: "I'm surprised at that comment from him ... Nobody goes on that painful journey for the fun of it."