The sadistic boy king, choked to death this week in the episode during his wedding to Margaery Tyrell, in a new shocking twist to the stunning medieval blockbuster which has become one of the biggest ever shows on TV.
The death of the child king in the ‘Purple Wedding’ episode has caused huge ripples among the HBO hit’s huge worldwide audience.
The modest Cork star revealed late last year that he would be turning his back on celebrity and walking away from a promising career in Hollywood when his run as one of the show’s most evil characters ended.
George RR Martin, author of the ‘Song of Ice and Fire’ series on which Game of Thrones is based, told Entertainment Weekly he hoped the 21-year-old hasn’t turned his back on acting as he believes he could be a Hollywood star.
"I hope that playing Joffrey didn’t help make him want to retire from the profession because he does have quite a gift for it and could have a major career as an actor.
"He’s very perceptive and he played this loathsome character and somehow made him more loathsome. He created someone that everybody hates, and loves to hate, and that’s a considerable feat of acting. I feel a little guilty that he’s quitting acting now."
The writer was full of praise this week for the young Irish actor who leads a normal life as a student in Trinity, where he is reading philosophy and theology.
Gleeson revealed recently he would like to move into working behind the scenes in theatrical productions after his final scenes in Game of Thrones, which is filmed in Northern Ireland.
Martin said the actor is the complete opposite of King Joffrey.
"I think Jack was sensational. I met Jack during the filming of the pilot many years ago now, and he’s like the nicest guy you’d ever want to meet. He’s really bright and a fiercely intelligent young man."
He said the Irish actor managed to make Joffrey even crueller than he was on the pages of his books.
"Jack has brought some incredible acting chops to the role that somehow makes him even more loathsome than he is on the page."
Rolling Stone magazine named the death as the most seminal pop culture moment this week, ahead of Bubba Watson’s Master victory.
The poisoning of the child king was at the top of the list of the top 20 pop-cult power players. Time magazine even featured a banner headline asking ‘What’s Next For That Actor From Game of Thrones?’.
Meanwhile, Martin said he wanted the audience to feel a glimmer of sympathy for the 13-year-old child king as he is dying despite his malevolence.
He said: "I think Joffrey is a classic 13-year-old bully. Do you know many 13-year-old kids you’d like to give absolute power to? There’s a cruelty in children, especially children of a certain age, that you see in junior high and middle school.
"There’s kind of a moment there where he knows that he’s dying and he can’t get a breath and he’s kind of looking at his mother and at the other people in the hall with just terror and appeal in his eyes, ‘Help me mommy, I’m dying.’
"I didn’t want it to be entirely, ‘Hey-ho, the witch is dead’. I wanted the impact of the death to still strike home on to perhaps more complex feelings on the part of the audience, not necessarily just cheering."