Complex sentence: When Stannis suspected the parentage of Queen Cersei Lannister's children, he brought his suspicions to Jon, who confirmed that Cersei's children were fathered not by Robert but by her brother Jaime.
Split into simpler sentences: When Stannis suspected the parentage of Queen Cersei Lannister's children, he brought his suspicions to Jon. Jon confirmed that Cersei's children were fathered not by Robert but by her brother Jaime.