Complex sentence: The identity of Duncan's mother is given by the Orkneyinga saga, which records the marriage of Malcolm and Ingibiorg, and then mentions "their son was Duncan, King of Scots, father of William".
Split into simpler sentences: The identity of Duncan's mother is given by the Orkneyinga saga. Which records the marriage of Malcolm and Ingibiorg, and then mentions "their son was Duncan, King of Scots, father of William".