Following on from news that renowned fantasy author Sir Terry Pratchett OBE has died, several writers and celebrities took to Twitter to express their sadness at his passing.

Neil Gaiman, who worked with Terry Pratchett on Good Omens

He was my friend for thirty years and a month. I miss him. Donate to Alzheimer's research and make it so things like this don't happen.

— Neil Gaiman (@neilhimself) March 12, 2015

Matt Haig, author of The Humans

Oh balls and bugger. Terry Pratchett. True storyteller. Brilliant, damn funny writing too. Leaves a world for us to live in.

— Matt Haig (@matthaig1) March 12, 2015

Val McDermid, author of The Mermaids Singing

The world is a less fantastic place tonight. RIP Terry Pratchett.

— Val McDermid (@valmcdermid) March 12, 2015

Margaret Atwood, author of The Handmaid's Tale

Very sad to hear of the death of #terrypratchett. I vastly enjoy his playful, smart #Discworld books.

— Margaret E. Atwood (@MargaretAtwood) March 12, 2015

Patrick Ness, author of A Monster Calls

Discworld is one of the very most fabulous creations in all of literature. I am gutted by the death of Terry Pratchett. One of a kind.

— Patrick Ness (@Patrick_Ness) March 12, 2015

David Cameron, UK Prime Minister

PM: Sad to hear of Sir Terry Pratchett's death, his books fired imagination of millions & he fearlessly campaigned for dementia awareness.

— UK Prime Minister (@Number10gov) March 12, 2015

Ricky Gervais, comedian, actor, producer

"It’s not worth doing something unless someone, somewhere, would much rather you weren’t doing it." RIP the brilliant Terry Pratchett.

— Ricky Gervais (@rickygervais) March 12, 2015

Spencer Kelly, presenter

Farewell Terry Pratchett. Thanks for painting my teenage years all 8 colours of the rainbow.

— Spencer Kelly (@spenley) March 12, 2015