Sir Paul McCartney has admitted working with other musicians is a let-down after his partnership with John Lennon.
McCartney said he and Lennon "knew each other's minds"
Speaking to BBC 6 Music, the 64-year-old singer said he was "a little bit spoiled" by starting his career with Lennon.
"I'm a little bit wary of collaborating with other people because it doesn't happen as easily or as amazingly as it did with John," he added.
Sir Paul and Lennon first met as teenagers in Liverpool.
They went on to form one of the most successful and influential songwriting partnerships in musical history.
Sgt Pepper anniversary
Since the break-up of the Beatles, Sir Paul has worked with many artists including Stevie Wonder and Michael Jackson.
But he admitted nothing quite matched writing with Lennon.
"It's a funny subject the collaboration thing because I collaborated with John and you're a little bit spoiled after that.
"That was one hell of a collaboration.
"I've done it quite a bit since and, I think - and I hate to say it - there's inevitably a sense of disappointment because it was just so cool for John and me to be working together, because we started so young and knew each other's ways and minds."
BBC 6 Music is to dedicate a day to The Beatles' Sgt Pepper's Lonely Hearts Club Band album to mark its 40th anniversary.
BBC Radio 2 will also broadcast a special re-recording of the classic album by contemporary artists.