Broadcaster Sir David Attenborough says he is glad his got his knees done because it means he can go on making nature programmes.
Sir David, who will be 90 in May, told the Daily Mail Weekend magazine: "I had one done. They (the doctors) weren't keen on doing both at the same time, which I would have liked because I was in my eighties. They don't want to keep you on anaesthetic for that long. It was a nasty business.
"Not fun. I thought, "I'm not going through that again." But then the other one started playing up and I realised that if I wanted to go on making programmes I'd better be able to walk.
"Now I can walk for an hour. I shall be going off to Patagonia in a couple of weeks where we're doing a film on a huge dinosaur that's being excavated."
Sir David had found he could only hobble around for a few yards as his old knees were unable to support him.
The much-loved natural world presenter, whose shows include The Blue Planet, Planet Earth and Frozen Planet along with a new series The Hunt, said: "I'm doing what I've done for the past 30 years. It's only the fun that keeps me going. If I didn't enjoy it I would stop. I've got a pension."
Sir David politely dismissed a comment by outspoken adventurer Bear Grylls, 41, that Sir David's personal style is "a bit dry" for today's young viewers and that it "needs that adventure".
Sir David said: "The natural world is wonderful enough. You don't have to distort anything.
"What's out there is so beautiful, so absorbing and so stunning, if you present it honestly there's no need to over-sentimentalise it, no need to make it more awesome than it is. Let it speak for itself. This world is good enough for me, thanks."
His brother Lord Attenborough, the actor and Oscar-winning film director whose films included Gandhi and A Bridge Too Far, died in August 2014.
Sir David told the Daily Mail Weekend magazine: "'He fell down the stairs and damaged his brain and was in a coma for a long time. He never really recovered and it was tough."
Lord Attenborough had been confined to a wheelchair and unable to read or write but was able to recognise his brother.
Sir David visited him regularly to chat and share jokes but it was all "very distressing," he recalled.