Rue was one of Ashildr and Tomas' two sons, the other being Johann.
After giving birth to Essie, Ashildr, using the alias "Alys", decided to have two more children, Johann and Rue, so that they can comfort one another on the day Ashildr would leave them to protect her secret.
Ashildr, having become wary of Tomas's growing comments related to her immortality, decided to leave him and take their children with her on a boat to England in 1348, where Rue and his siblings caught the bubonic plague. Ashildr tried to decide which one of them to save with the second Mire medical patch, but ultimately decided to let all three of them die. (PROSE: The Triple Knife) Afterwards, Ashildr kept in pages to remind her to never have offspring again as they would all die eventually.