Ok. This is for you, Lioness99a (and everyone else, of course). (It's word for word. Nothing's missed out, or added in.)
He's already conquered the world of TV in shows like Torchwood and Hustle, he's a singing star - and now the entertainer has teamed up with his big sister Carole to write their first novel, Hollow Earth, a children's book set in Scotland about a brother and sister with mystical powers who could hold the secret to saving the world. Although the pair have collaborated on writing John's autobiographies before, this is the first time they've reached into the realms of fantasy fiction
"It was great. when we first started plotting the book I was driving to Cardiff, Carole was in the passenger seat and we had both eaten a LOT of Percy Pig sweets so our imaginations were flying!" He laughs.
John, who spent his early years in Scotland before the family relocated to America, points out that it's much more than simply a book - it's a tribute to their family and early days spent in a country they both love.
"While writing the book we went back to our childhood and we did that in order to honour our heritage and pay tribute to our roots," explains John. "The character Jeannie is based on my gran's sister who used to look after us. And Sandy - the twins' feisty mother - is to honour my partner Scott's sister who died of brain cancer five years ago.We made her a heroic mother in the book because that's what she was. There's a lot of family influence in the book."
Indeed, the mythical island of Auchinmurn where much of the book is based is actually the island of Cumbrae on the west coast of Scotland. They renamed the island as a touching tribute to their beloved Granny Murn.
"Like many kids from Glasgow, we'd often take day trips from the city on the train with Mum and Jeannie and Murn and we'd go to Largs and take the ferry over to the island," says Carole. "The place has a very nostalgic feel for us."
Just like any brother and sister, the pair admit they fought like cat and dog when they were growing up...
"She was a nightmare," laughs John. "She almost killed me... twice! One time I was just a baby and she was meant to be looking after me - when my parents arrived home I was nearly choking to death. She's tried to feed me three packets of crisps to stop me crying!"
Hopefully things are better nowadays?
"It's a lot of fun working together - there have been times in the car when we've had to pull over to get purselves under control because we're laughing so much," explains Carole.
John agrees that as adults they are far closer.
"There are eight years between Carole and me, which is a lot when you're kids so we didn't hang out that much," says John. "Now, as adults, we've become very close and have kind of reverted back to childhood to relive a time that the age gap didn't allow back then. The good thing is, now we get to have a glass of wine!"
Hollow Earth by John and Carole E. Barrowman (Buster Books, £6.99) is available to buy now. Look up the Hollow Earth website http://www.hollow-earth.co.uk for more information about the book.