Simplify the following text for a Grade 5 native English-speaking person.
Original: When he was twelve , he became Grand Prince Chungnyeong ' and married a daughter of Shim On of Cheongsong , commonly known as Lady Shim , who later was given the title Queen Soheon .
Simplified: When he was twelve , he became grand prince and married Shim On of Cheongsong .