Paul McCartney is the real "Grandude" of book signing

He may be one of the world's most famous musicians, but Paul McCartney is also just a regular grandfather - and that is the experience he draws on for his new children's book "Hey Grandude!".

While the title is a nod to one of The Beatles' best-known songs, "Hey, Jude", it is inspired by a nickname given to McCartney, 77, by one of his eight grandchildren.

"One of them just said to me one day 'Hey grand dude'," the former Beatle told a group of schoolchildren from Jubilee Primary in Brixton at the launch in a London bookstore on Friday.

"I thought 'Oh, he said 'hey grand dude'. And I said 'Wait a minute, you normally call me grandad' and he said 'No I like the sound of gran dude'. So that is what inspired me to write the book."

Publishers Puffin describes the book as a wild and wonderful adventure with a twist of magic inspired by McCartney's own experience of being a grandfather.