Complex sentence: It is not certain whether Sigurd returned home with his father to Norway after the 1098 expedition; however, it is known that he was in Orkney when Magnus returned west in 1102 for his next expedition.
Split into simpler sentences: It is not certain whether Sigurd returned home with his father to Norway after the 1098 expedition. However, it is known that he was in Orkney when Magnus returned west in 1102 for his next expedition.