Complex sentence: Gwenllian grew to be strikingly beautiful, and after Gruffydd ap Rhys, the Prince of Deheubarth, ventured to Gwynedd around 1113 to meet with her father, she and Deheubarth's prince became romantically involved and eloped.
Split into simpler sentences: Gwenllian grew to be strikingly beautiful, and after Gruffydd ap Rhys, the Prince of Deheubarth, ventured to Gwynedd around 1113 to meet her father. She and Deheubarth's prince became romantically involved and eloped.