Complex sentence: The Starfleet officer who rescued Worf had been told by the Klingon government that he had no living relatives, but Kurn was taken in by his father's closest friend, Lorgh, and raised as his son.
Split into simpler sentences: The Starfleet officer who rescued Worf had been told by the Klingon government that he had no living relatives. But Kurn was taken in by his father's closest friend, Lorgh, and raised as his son.