The Office and EXTRAS star, who refers to the MATT GROENING-created show as "the greatest TV comedy of all time," admits he's still in shock at the opportunity to appear alongside his yellow heroes.
He tells the New York Daily News, "It was like I'd won a competition.
"I'm genuinely worried that Hollywood got together and talked to my doctors and found out I've only got a few months to live and said, 'Just let him do what he wants to do.'
"I'm in awe of (The Simpsons) and have been for at least 10 years.
"When I first got into comedy, my ambition was to get a joke on The Simpsons. So to write and star in one is ridiculous."
"Remarkably, I've got to a place where I'm cherry-picking jobs and I'm cherry-picking jobs (with) my heroes. I mean, really! The Simpsons!"
Gervais' episode airs on 26 March (06) and sees HOMER and long-suffering spouse MARGE picked for a wife-swap reality show.