Sigourney Weaver once wrote a 10-page fan letter to John Lennon.

The Avatar: Fire and Ash actress was a huge fan of the Beatles when she was growing up and she recalled dropping off a lengthy missive at a restaurant she had heard the singer - who was shot dead in 1980 - frequented.

Speaking on the Late Show with Stephen Colbert, she said: "I think I was too shy, but I did leave -- again for John Lennon -- I wrote a several-page letter on lavender stationery with purple ink, [which began] 'Dear John....'

"It was like five pages front and back. And I folded it up. I put an envelope, and I dropped it off at this restaurant that I heard he went to," she continued, putting her face in her hands out of embarrassment.

Sigourney insisted she couldn't remember what she wrote, but hoped it hadn't been handed over.

She said: "I hope they threw it away."

The 76-year-old star explained the Imagine hitmaker was her favourite Beatle because of his mischievous side.

She said: "I did kind of fall in love with John because I read … that he used to work at the airport, and for VIPs, he made a plate of sandwiches and, just before he sent them out, he'd put his shoe in them and then put it back together and put it on the platter.

"I thought that was so cool."

The Alien actress was around 12 years old when she saw The Beatles in action at California's Hollywood Bowl, but because she was surrounded by "screaming" girls, she "couldn't hear them at all".

The concert featured in Ron Howard's documentary, The Beatles: Eight Days a Week, with a young Sigourney visible in the crowd, even though she was "at the very back" of the venue.

She noted: "My hair is huge because I put it on beer cans all day, straightened it, and I'm wearing my one nice dress."

And after the show, Sigourney and her friend were stunned into silence when John and Sir Paul McCartney waved to them as their limousine passed by during their walk home.

She said: "We were so excited that we came so close -- we were like 10 feet away as the car went by -- that honestly, I think we both went home and just laid on our backs and looked at the ceiling for 24 hours."