The 32-year-old actor, who played Robb Stark for three seasons on the HBO epic fantasy drama, told Entertainment Weekly that he did not participate in the reunion, which was filmed earlier this year in Belfast near the end of production on eight season.
"I didn't do any of that. I was (filming) 'Rocketman' so I wasn't able to do that," Madden said.
The special will not air on HBO but will be exclusive to a new "Game of Thrones" Blu-ray box set of the entire series that will be released in the second half of 2019.
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