Zoella Girl Online book is fastest-selling debut novel

Video caption, Hayley looks back at Zoella's incredible 2014

YouTube star Zoella's first book has become the fastest-selling debut novel ever.

Girl Online sold more than 78,000 copies in its first week.

Zoella tweeted: "I'm legit blown away by this. I never in a million years thought that so many of you would pick up a copy of Girl Online. Almost want to cry."

She has more than 6.6 million followers on YouTube, where she posts beauty and fashion videos.

Video caption, Zoella tells Ricky how she's dealt with cyberbullying (February 2014)