Last week we were shocked to learn that 'Game of Thrones' season 4 had tapped 'Treme' star Michiel Huisman' to replace Ed Skrein in the prominent role of Daario Naharis, though it seems the George R.R. Martin-adapted HBO drama has made a mountain of another replacement. Icelandic actor Hafthor Julius Bjornsson will take over the role of Gregor "The Mountain" Clegane, a role that had itself already once been recast, so why all the change?

Bjornsson himself revealed the news over Twitter, saying "For all my fans! I am happy to tell you that I will be THE MOUNTAIN In season 4 In Game Of Thrones :)" This is the second time a new actor has been placed in the towering role, after Ian Whyte took up the role from Conan Stevens in season 2. The character had not appeared in season 3, but will take on a more prominent role in season 4 opposite cast newcomer Pedro Pascal's Oberyn "The Red Viper" Martell.

'Thrones' has a habit of recasting less prominent characters when it comes time for expanded roles, as was the case with David Michael Scott briefly portraying the role of Beric Dondarrion in season 1, before Richard Dormer assumed the expanded role in season 3. Season 4 will also see Dean-Charles Chapman assuming the increasingly prominent role of Tommen Baratheon, replacing young actor Callum Wharry, though in the case of both Daario Naharis and The Mountain, Huisman and Bjornsonn's castings will prove the most noticeable yet.

While we wait for ‘Game of Thrones’ season 4, HBO has cast in known roles Roger Ashton-Griffiths as Mace Tyrell, and Indira Varma as Oberyn's lover Ellaria Sand. ‘Sherlock‘ star Mark Gatiss has joined the series in an unknown part, while ‘Banshee‘ star Joseph Gatt will appear in a role speculated to be that of Wildling chieftan Styr, Magnar of Thenn. Previous season characters Lysa Arryn (Kate Dickie), Ser Alliser Thorne (Owen Teale), Rorge (Andy Beckwith) and Janos Slynt (Dominic Carter) will likely all return, among others.

We'll keep our eyes out for any other new faces on the road to 'Game of Thrones' season 4, but in the meantime, what say you? Does the fantasy drama's latest recasting have you on edge for more upheaval in season 4? Who else might be replaced before 2014? Check out the original Mountain in season 1 below, and give us your thoughts in the comments!

More From ScreenCrush