Where Have You Seen Joffrey's Brother Before? On 'Game of Thrones'!

·Writer, Yahoo Entertainment

Warning: This post contains character and storyline spoilers.

It's not the first "Game of Thrones" recasting — Michiel Huisman took over the role of Daario Naharis from Ed Skrein, and Hafþór Júlíus "Thor" Björnsson will be the third actor to play Gregor "The Mountain" Clegane, after Conan Stevens and Ian Whyte. But Dean-Charles Chapman's takeover of the role of Tommen Baratheon is unique: It's the second role the 16-year-old has played on the series.

[Related: 'Game of Thrones' Gaffe: Jaime Lannister Brought Coffee to Joffrey's Wedding?!]

The casual "GoT" viewer might have missed it, but Chapman previously played Martyn Lannister, the army squire who, along with his brother Willem, was murdered by Rickard Karstark in Season 3. Tracing out the Lannister family tree, Martyn was the son of Kevan Lannister, Tywin Lannister's brother. He was a first cousin to Tommen's parents, Cersei and Jamie. So Chapman is currently playing the first cousin once removed of the character he originally played on "GoT."

Kid actor Callum Wharry played Tommen in Seasons 1 and 2, but, as Chapman confirmed in a red carpet interview before the Season 4 premiere, Tommen plays a bigger role in Season 4. And as readers of the "Game of Thrones" books know, a slightly older actor playing the role is more appropriate for some of the action that lies ahead. Now that King Joffrey has been permanently dethroned, little brother Tommen, who Chapman describes as "a nice kid," is next in line to sport the crown.

More scoop on Chapman: His résumé also includes the Golden Globe-nominated miniseries "The White Queen," the title role in the British sci-fi sitcom "The Revolting World of Stanley Brown," the title role in a West End production of "Billy Elliot the Musical," and roles in the upcoming big-screen comedy "Man Up," with Simon Pegg, and "Before I Go to Sleep," a thriller with Nicole Kidman and Colin Firth.

[Related: A 'Game of Thrones' Whodunit: The Suspects for That Shocking Murder]

As he told Vulture, he was surprised to learn just how prominent a role Tommen would play in Season 4.

"I was like, 'Whoa!'" he said. "I know it sounds silly, but I hadn't read the scripts, and I didn't know what had happened. And then I flew over to Belfast so they could dress me for wardrobe, and the lady said, 'OK, let's get your crown on.' And I was like, 'Crown?' 'Yeah, you know, you're going to be king!'

"So I just stood there, looking in the mirror, with this thing on my head, stunned."

"Game of Thrones" airs Sundays at 9 p.m. on HBO.