Riannon was the orphaned daughter of Lara Dorren and Cregennan of Lod, and thus the 4th great-grandmother of Ciri. Cerro, the queen of Redania at the time, adopted her soon after her birth and named her. When she was 17, her beauty was well known and many ruling houses vied for her hand in marriage. Out of them, Riannon married Goidemar, the king of Temeria.
Three years later, Falka's rebellion broke out and a pregnant Riannon was imprisoned and gave birth to twins, Fiona and Amavet, and went mad. That did not stop Falka from giving her own newborn daughter to the prisoner to nurse, though. When the rebellion was quelled, Riannon returned to her husband, but with three children in tow. Due to her insanity, Riannon was unable to tell which one of the children was not hers and, when she finally did recover, she couldn't remember much that'd happened during her imprisonment. Despite this, Goidemar and Riannon eventually raised the three as their own.
However, roughly 18 years later, she died at 38 years old, believed to have been overcome with grief after the death of two of her children, Amavet and Adela, within a year's time.
Riannon share a similar name to the Welsh heroine Rhiannon, a prominent character of the Mabinogi and a goddess of the underworld.
↑ 1.01.1Later information dug up by Fenn would suggest that Fiona was actually Falka's daughter, not Adela.