How to unlock Harry Potter Easter eggs on social media

Facebook has launched an Easter egg which fills users' screens with sparks from a wand to mark the 20th anniversary of the release of Harry Potter and the Philosopher's Stone.

The first hardback run of JK Rowling's series, on 26 June 1997, was just 500 copies.

It's now sold more than 450 million books around the world.

Twitter has got on board too by making a special emoji of Harry's trademark glasses.

Here's how you get them.

On Facebook all you have to do is type "Harry Potter" into a status or comment, followed by the name of one of Hogwarts' houses.

In case you've forgotten - you've got four to choose from: Gryffindor, Hufflepuff, Ravenclaw and Slytherin.

The text will then change colour and when you click on it a wand will appear and shoot sparks across the screen.

On Twitter, an emoji appears when people type the hashtag #HarryPotter20.

Fans have been using it to share their memories of the series.

Alfonzo posted an "every day I'm Dumblin" meme. "Today, in 1997, a book about a boy wizard was first published, and the world changed forever. Happy 20th to #HarryPotter", he wrote.

Victoria said: "Happy book birthday to the philosopher's stone". She included a gif of Hogwarts students throwing their hats into the air.

Saytanim uploaded a photo of the birthday cake Hagrid gives to Harry in the first film.

Janvi said: "Once a Potterhead, always a Potterhead".

Of course, there aren't just JK Rowling's books to talk about. The series also spawned one of the most successful film franchises ever.

The final instalment, Harry Potter and the Deathly Hallows Part 2, is the eighth-highest grossing movie of all time.

The franchise continued in 2016, with the spin-off Fantastic Beasts and Where to Find Them.

JK Rowling says she has plans for five more Fantastic Beasts films.

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