Later in season seven, Samwell interrupts a meeting of the Conclave, the collective Archmaesters, as they discuss a raven sent by Bran Stark about the army of the dead. They don't want to heed Bran's warning, but Samwell attempts to convince them the wights and White Walkers are real. Frustrated by the Conclave's lack of action, Sam returns to his room where he helps Gilly with her reading, which just happens to be the journal of High Septon Maynard. The two discover that Prince Rhaegar's had his first marriage annulled and that he secretly remarried while in Dorne. However, the information doesn't resonate until after Sam decides to leave the Citadel and travel to Winterfell where he reunites with Bran Stark.
After learning of Bran's new powers as the Three-Eyed Raven, Sam confesses his desire to help Jon win the war against the Night King. Bran counters revealing Jon is actually the son of Rhaegar Targaryen and Lyanna Stark. At that point, Sam recalls the passage Gilly read to him from the High Septon's journal and together they realise that Robert's Rebellion grew from a lie since Jon is the true heir to the Iron Throne.