Complex sentence: During the battle, Eragon sights a flying figure, which he had earlier mistaken to be a Lethrblaka, though actually it turns out to be a red dragon, probably hatched out of one of the two eggs that Galbatorix had in his possession.
Split into simpler sentences: During the battle, Eragon sighted a flying figure, which he had earlier mistaken to be a Lethrblaka. Actually it turned out to be a red dragon, probably hatched out of one of the two eggs that Galbatorix had in his possession.