Daniel Radcliffe, the lead star of the original "Harry Potter" film franchise, is remembering his late costar Michael Gambon after Gambon died of pneumonia this week at age 82.

"Very sorry to hear about the passing of Michael Gambon. He was, on and off the camera, a legend," Radcliffe wrote on his verified Instagram on Thursday, alongside a touching video montage showing Gambon portraying Hogwarts headmaster Dumbledore in the "Harry Potter" movies.

Radcliffe also included a quote from Dumbledore in his caption: "Happiness can be found even in the darkest of times, if one only remembers to turn on the light."

Rupert Grint, who portrayed Ron Weasley in the films, also posted a tribute to Gambon on Instagram, writing, "So sad to hear about Michael. He brought so much warmth and mischief to every day on set. He captivated me as a kid and became a personal role model of mine for finding the fun and eccentricities in life."

Gambon portrayed Dumbledore in six of the eight "Harry Potter" films, a role he took up following the death of Richard Harris in 2002.

"Harry Potter" author J.K. Rowling also took time to remember the actor on Thursday, writing on X/Twitter, "I've just heard the awful news about Michael Gambon. The first time I ever laid eyes on him was in King Lear, in 1982, and if you'd told me then that brilliant actor would appear in anything I'd written, I'd have thought you were insane."

"Michael was a wonderful man in additional to being an outstanding actor, and I absolutely loved working with him," she added.

Actor Jason Isaacs, who played Lucius Malfoy in the "Potter" films, called Gambon "magnificent" in his tribute on X/Twitter, continuing, "I learned what acting could be from Michael in The Singing Detective - complex, vulnerable and utterly human. The greatest thrill of being in the Potter films was that he knew my name and shared his fearless, filthy sense of fun with me."

Gambon died at 82 following a "bout of pneumonia," a statement issued on behalf of his family said on Thursday, PA Media news agency reported.

"We are devastated to announce the loss of Sir Michael Gambon," the statement issued by his publicist Clair Dobbs said, according to PA.