 Sigtrygg married Brian Boru 's daughter , Sláine , and they had one son : Olaf ( d . 1034 ) . According to the Annals of the Four Masters , Olaf " was slain by the Saxons " on his way on a pilgrimage to Rome . He was survived by one Ragnhild , from whom Gruffudd ap Cynan and the Kings of Gwynedd were descended . 
