JK Rowling has led the Twitter reaction to a very special day in the Harry Potter universe.
This day, September 1 2017, is a day marked in the epilogue of the final book in the series, Harry Potter and the Deathly Hallows.
It's the day that Harry Potter's son, Albus Severus, goes off to Hogwarts.
Appropriately, there have been gatherings in King's Cross - where the train to the school leaves from Platform 9 3/4 - and #19YearsLater has been trending on Twitter.
See the reaction here: