Simplify the following text for a Grade 6 native English-speaking person.
Original: The son of Frederick II , king of Denmark-Norway , and Sofie of Mecklenburg-Schwerin , he was born at Frederiksborg castle in 1577 .
Simplified: Christian was the son of Frederick II , king of Denmark-Norway , and Sofie of Mecklenburg-Schwerin . He was born at Frederiksborg castle in 1577 .