Roald Dahl is one of the world's best-loved children's authors. He died nearly 20 years ago but the popularity of his books and poems is still celebrated every year on his birthday - 13 September.
As part of the celebrations this year, illustrator Chris Riddell was invited to create a new poster for The BFG in the window of a London book shop.
Passers-by stopped to watch as Chris brought the huge blank boards to life with his illustrations of the BFG and the Bloodbottler and Bonecruncher giants.
He included another essential character on the poster too, but can you see who it is?
It was Sophie hiding behind the BFG's ear. Did you know Sophie's character was based on Roald Dahl's granddaughter?
Chris said he loved the giants in The BFG - like this Bonecruncher - but his fave Roald Dahl books were Charlie and the Chocolate Factory and James and the Giant Peach.
It took him less than an hour to draw this huge outline of all the characters, but then it was time to colour them in.
Chris said he couldn't find his own coloured pencils before he left home so he had to borrow his daughter Katy's.
The massive window poster was finished in about two hours, but what advice would Chris give to any of you who fancy designing their own posters or book covers?
"Don't worry about what's been done before," he said. "Try out a few designs and choose one bold, eye-catching central image - something that would make you stop to pick it up in a book shop."