On Tuesday - the 24th anniversary of Harry's first departure to the magic school that was Hogwarts - Rowling sent out a tweet via her Twitter account.
"Could somebody at King's Cross wish James S. Potter good luck for me?" she tweeted.
"He's starting at Hogwarts today."
James S. Potter is the oldest son of Harry and Ginny Weasley.
A few hours later, she continued with the fun.
"Now worried that he'll be irritated by the number of people saying hi."
Another tweet, sent at the end of the day, says: "Have just heard that James S Potter has been Sorted (to nobody's surprise) into Gryffindor. Teddy Lupin (Head Boy, Hufflepuff) disappointed."
Rowling's posts - which have been retweeted almost 200,000 times - are a cheery epilogue to the final book in the seven-book Harry Potter series.
At the end of Harry Potter And The Deathly Hallows we learn that, 19 years on, Harry and Ginny have three children: James Sirius, Albus Severus and Lily Luna.
The book's last words indicated Harry had put the troubles of his early life behind him when it said: "The scar had not pained Harry for nineteen years. All was well."