Sir Cliff Richard has revealed that he has told his family not to "let it go on too long" if he develops dementia.
The 71-year-old singer discussed the illness with one of his sisters after they watched their late mother suffer from Alzheimer's disease.
He told Radio 4's Woman's Hour that he and his sister made a pact to look after each other if either of them developed dementia.
"I have discussed it with my sister. I said, look if this happens to me... I'll do the same for you if you'll do it for me, don't let it go on too long," Sir Cliff said. "And just make sure I'm looked after because I don't want to be a burden on anybody else."
He said: "If it happened when I was 90, 20 years from now, they might well have allowed euthanasia or something like that. Dementia does not take your life - but it removes it away from you. You don't have a life. It just stops you living."
Sir Cliff's mother Dorothy died in 2007 at the age of 87, after a decade-long battle with Alzheimer's.
Speaking of his mother's illness, he said: "It was a gradual change to start with but then it steamrollered at the very end. In the last three or four years she came to a point where she really didn't know who I was.
"If she referred to me, she'd call me 'that Cliff Richard' and she'd be looking at me. She had to be looked after like a baby... She stopped being the woman we knew."
The star, who became a patron of the Alzheimer's Research Trust in 2002, said the illness had not led him to question his faith in God. He said: "We're all going to die somehow of something at some time. And my mother was 87. I don't question my faith about that kind of death."
"I did question God a lot when (TV presenter) Jill Dando got murdered. I had never had a friend or anybody that I knew that had actually got shot and killed. It just seemed ridiculous... It was a useless death. So I spent a lot of time being angry with God."