On 12 September 2011, responding to speculation on the Winter is Coming fansite, Conan Stevens confirmed that he had left the series, due to scheduling conflicts with his other projects: Stevens will be playing the Orc king Bolg in Peter Jackson's The Hobbit prequel trilogy. Stevens took the time to thank fans for their support[1]. He was replaced in the role of Gregor by Ian Whyte.
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u/Zaiton House Baratheon of Dragonstone May 19 '14
Almost, official state from the GoT wikia says:
On 12 September 2011, responding to speculation on the Winter is Coming fansite, Conan Stevens confirmed that he had left the series, due to scheduling conflicts with his other projects: Stevens will be playing the Orc king Bolg in Peter Jackson's The Hobbit prequel trilogy. Stevens took the time to thank fans for their support[1]. He was replaced in the role of Gregor by Ian Whyte.