Three new characters will be added to the new season:
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The first new character is Oberyn Martell, who is a prominent member of the Martell family. During “Game of Thrones” Season 2, Tyrion Lannister made a deal with the Martells and sent his niece, Myrcella Baratheon to the Martell stronghold in Dorme for her safety and an arranged marriage to seal their alliance.
Mace Tyrell is the second new addition, who was briefly mentioned earlier in the third season by his mother, Lady Olenna Tyrell; who had nothing flattering to say about him. Mace is the father of Loras and Margaery Tyrell.
Finally, the last confirmed addition is the Magnar of Thenn, who is one of the greatest warriors in the Wilding army led by Mance Rayder.
Credit: Towerofthehand.com