AceShowbiz -

J.K. Rowling turned 50 on Friday, July 31. To celebrate her birthday, TIME magazine invited some "Harry Potter" stars to give her birthday messages and Matthew Lewis, who played Neville Longbottom in the famous franchise, wrote a touching letter to the author.

"I could talk about the millions of lives Jo has enriched whether through the stories and characters she's created or through the millions of pounds she's given to charity," Lewis wrote. "She's a remarkable woman. However, I would like to thank Jo for changing MY life. Without her imagination and her talent I would never have become the man I am today."

"That's not even to mention her generosity and loyalty when it has come to supporting everything that I have done in the years since Harry Potter," the 26-year-old actor added. "She's just wonderful human being and I consider myself so privileged and honored to call her a friend. Happy birthday, Jo."

As a reply to people who gave her best wishes on her birthday, Rowling tweeted, "Thank you so much to everyone wishing Harry and me a happy birthday! I'm having a wonderful time in the sun with family and friends. xxxxx."

Earlier this year, Lewis and Rowling had a hilarious Twitter exchange following his sexy photo shoot for Attitude magazine. "Not as bad as watching Dan[iel Radcliffe] in Equus, but close. Warn me next time, for God's sake," Rowling tweeted to Lewis. "Well, this is awkward. Sorry, Jo," he replied, to which she jokingly wrote him back, "I will always support you whatever you want to do, Matthew. Now go put some clothes on."