Complex sentence: Gingalain is the son of Sir Gawain by Blanchemal, a fay that he meets in the forest, but his mother never tells him about his lineage.
Split into simpler sentences: Gingalain is the son of Sir Gawain by Blanchemal, a fay that Gawain meets in the forest. Blanchemal keeps Gingalain's identity a secret from him and never tells him about his lineage.