Daemon's relationship with his first wife, Lady Rhea Royce, comes about as an arranged marriage at the behest of his grandmother Queen Alysanne when he is only 16 years old. Although the marriage is a good fit in terms of rank, with Rhea serving as the heiress of House Royce at the time, "Fire & Blood" describes the marriage as not a happy one.
According to the book, the couple have no children together, and they are soon bitterly estranged, but they remain married for nearly 20 years. Rhea dies after an apparent riding accident, and Daemon is unwelcome in her home of the Vale afterward. "House of the Dragon" gives more insight into Rhea's death.
At the beginning of episode five, Daemon visits Rhea at the Vale while she's hunting on horseback. As they converse, Rhea reveals they never consummated their marriage and berates him, establishing that they are, in fact, bitterly estranged. Daemon then purposely intimidates Rhea's horse, causing it to buck up and throw her off its back. Upon landing, she's unable to move, suggesting her spine was injured in the fall. Daemon then picks up a rock before we abruptly cut to the next scene, suggesting he bashes her head with the rock, killing her.
Why Did Daemon Kill Rhea?
Before Daemon intimidates Rhea's horse, she criticizes him for having been passed over as heir to the Iron Throne for Rhaenyra. At one point, she asks him, "What will you do now? Will you strike [Rhaenyra] down? Or . . ." She then trails off, coming to an unspoken realization before reaching for her bow. Unfortunately, Daemon intimidates her horse before she gets a chance to defend herself.
It's likely Rhea realized on her own that Daemon had no intention of striking Rhaenyra down, but instead had hoped to marry his niece — making Rhea an obstacle to his grand plans. It seems he killed her to clear the way for his next marriage, and the fact that he would inherit Runestone in the process sweetened the deal.
