The Brothel Queens was the nickname used by Archmaester Gyldayn to refer to one of the stories told by Mushroom in his Testimony. It concerns the Dowager Queen Alicent Hightower and her daughter, Queen Helaena Targaryen.
After the fall of King's Landing, the Dowager Queen Alicent Hightower begged Queen Rhaenyra Targaryen to settle for peace with Aegon II Targaryen. During the exchange between the two queens, Alicent made reference to an old rumor stating that Rhaenyra's sons were not her late husband's legimate children but the bastards from one of her favorites.
According to Mushroom, Mysaria, Rhaenyra's mistress of whisperers, dissuaded her from taking the queen's tongue and instead suggested a more terrible punishment: Alicent and her daughter, Queen Helaena, should be sent to a brothel in King's Landing where the two queens would be forcibly impregnated. Moreover, Mushroom cited this event as the cause of Helaena's suicide.
The story of the "Brothel Queens" was popular in the taverns of the capital. Gyldayn entertained the possibility of Aegon II himself spreading the tale to further ruin Rhaenyra's image and spread rumors of her cruelty.
Let them remain there until they are with child. They speak of bastards so freely, let them each have one for their very own.