You know, for an HBO series whose source material has been available in book stores for over a decade, 'Game of Thrones' has become increasingly uptight with its casting. The latest to join season 4 of the HBO fantasy-drama in yet another mystery role is none other than 'Nashville' and 'Treme' star Michiel Huisman, so why all the secrecy?

New of Michiel Huisman's casting first arrived over Instagram, wherein the actor's personal trainer posted a photo of Huisman working out for the role, suggesting at least a strongly physical approach. The Dutch Huisman's casting is the latest mystery addition to 'Game of Thrones' season 4, following 'Banshee' star Joseph Gatt in a role speculated to be that of Wildling chieftan Styr, Magnar of Thenn, and 'Sherlock' star Mark Gatiss in an unknown part.

While we wait for ‘Game of Thrones’ season 4, HBO has cast in known roles Roger Ashton-Griffiths as Mace TyrellPedro Pascal as Prince Oberyn “The Red Viper” Martell, and Indira Varma as his lover Ellaria Sand. ‘Mad Men‘ star Christina Hendricks expressed her interest in joining the HBO drama after AMC closes Sterling-Cooper’s doors next year, though we don’t hold much hope for that. 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.

Hopefully HBO will lift the veil on Michiel Huisman's 'Game of Thrones' season 4 casting soon, but what say you? Which of George R.R. Martin's characters would the 'Treme' star seem most likely to fill?