HBO is reuniting with Michiel Huisman.

The Treme alum has joined the cast of the premium cable network's Game of Thrones, The Hollywood Reporter has confirmed. HBO is keeping who Huisman will play under wraps, but sources tell THR he will replace Ed Skrein and play Daario Naharis.

Word of Huisman's casting first surfaced on Instagram, where his trainer posted a photo of the actor bulking up to prepare for Thrones.

The actor, who most recently recurred on ABC's Nashville as a love interest for Rayna (Connie Britton), joins Thrones' growing season four cast that includes Joseph Gatt -- whose role also is being kept under wraps. Fan speculation (fueled by Gatt's IMDB page) has him pegged as Styr, Magnar of Thenn, the wildling leader known for his muscular build and hairless body.

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In A Storm of Swords, the third book in Thrones author George R.R. Martin's A Song of Ice and Fire, Styr leads an attack on Castle Black as part of Mance Rayder's assault on the wall. Martin has said Styr will have a role in season four, as well as other new characters Mace Tyrell (father of Margaery and Loras) and Oberyn Martell (better known as The Red Viper – a man with a vendetta against the Lannisters). The latter two roles already have been cast, with Roger Ashton-Griffiths taking on Mace Tyrell and The Red Viper going to Graceland actor Pedro Pascal.

Also on board for Thrones' fourth season is Rome's Indira Varma, who will play The Red Viper's love interest Ellaria Sand; and Sherlock's Mark Gatiss, whose role is also being kept under wraps.

The role marks a reunion for Huisman with HBO, following his starring role on Treme. (The final season of the series returns in December.) Huisman, whose credits also include World War Z, is repped by ICM Partners, Principal Entertainment in New York and attorney Frank Stewart.

E-mail: Lesley.Goldberg@THR.com

Twitter: @Snoodit