Complex sentence: Aegon Targaryen, nicknamed "Egg" in his youth, was called Aegon the Unlikely because he was unlikely to inherit the throne of the Seven Kingdoms, but was named king when a council bypassed those before him in the line of succession.
Split into simpler sentences: Aegon Targaryen, nicknamed "Egg" in his youth, was called Aegon the Unlikely because he was unlikely to inherit the throne of the Seven Kingdoms. Aegon V was later named king when a council bypassed those before him in the line of succession.