Paul McCartney writes his first children's picture book, 'Hey Grandude!'

Paul McCartney has written his first children's picture book.

"It's called 'Hey Grandude!' " said the pop-music legend, 76, Thursday in a video from publisher Puffin Books. "Why? Well, I've got eight grandchildren and they're all beautiful, and one day one of them said to me, 'Hey, Grandude.' . . . I thought, 'I kind of like that.' So from then on I was known as Grandude. So I thought, 'You know what, it's actually a nice idea for a book.' "

Illustrated by Kathryn Durst and scheduled for publication in the United States on Sept. 5, 2019, "It's about a character called Grandude who represents grandfathers everywhere," McCartney explained, "and he has four grandchildren . . . and they go on adventures with him. And he's kind of magical."

His first children's book, "High in the Clouds," with co-authors Geoff Dunbar and Philip Ardagh, was published in 2005.