An anonymous letter written by a teenager and left in a library book for the next reader to discover has gone viral on social media.

East Anglian Daily Times: William Court (9) found a letter in his library book from a previous reader. William is pictured at home in Haverhill.William Court (9) found a letter in his library book from a previous reader. William is pictured at home in Haverhill. (Image: Archant)

Krystal Vittles thought a tatty bookmark had been left in the copy of Raven’s Gate by Anthony Horowitz which she picked up at Bury St Edmunds Library to take home for her nine-year-old son William Court.

East Anglian Daily Times: William Court (9) found a letter in his library book from a previous reader. William is pictured at home in Haverhill.William Court (9) found a letter in his library book from a previous reader. William is pictured at home in Haverhill. (Image: Archant)

But it turned out to be a note from a teenager who is a fan of Anthony Horowitz novels.

Ms Vittles, 30, who works for Suffolk Libraries, did not let on she knew about the mystery letter, which William was then able to discover for himself.

James Powell, marketing and communications manager for Suffolk Libraries, said a picture of the letter had had 21,400 views on the Suffolk Libraries Facebook page and more than 300 likes.

He added the book’s publisher Walker Books tweeted the author about it and he replied: “this teenager may have started a trend”.

Ms Vittles said: “I just thought it was a really special thing to find. Because I work for the library service I can understand the value of finding something like that and how special it is. It was fabulous.”

William, who attends Place Farm Primary Academy in Haverhill, said: “I was a bit surprised really. I wouldn’t normally find a letter in the books I read.”

The mystery teenager says it has always been on their “bucket list” to write such a letter and they thought it would be a fun thing to do.

The letter says: “Sorry if you thought MI6 was trying to recruit you, now that would be exciting.

“Nope just a teenager enjoying life and trying to make people reading brilliant books smile.”

They go on to recommend some of their favourite authors.

Ms Vittles, from Haverhill, said the letter was especially lovely because it was by a young person.

“Young people do sometimes get a little bit of a bad name. I just thought it was such a lovely thing for someone to do. It’s made so many people smile and it really has gone viral.”

She hoped it would inspire more young people to take up reading for pleasure, and added William was talking about penning his own mystery library letter.