Who is Shubbiluliuma and Shubattu from Sinuhe the Egyptian: A Novel and what is their importance?

Shubbiluliuma is the King of Hatti. His name brings dread in his city of Hattushash. He never appears in public, and he has reigned for 28 years when Sinuhe visits. During the troubled transition following the death of Pharaoh Akhnaton, Shubbiluliuma sends his son and heir, Shubattu, to marry Princess Bakematon. Sinuhe is sent to intercept Shubattu in the Sinai and kill him without raising suspicion.