Simplify the following text for a Grade 10 native English-speaking person.
Original: Henry FitzRoy , 1st Duke of Richmond and Somerset ( 15 June 1519 â `` 23 July 1536 ) was the son of King Henry VIII of England and his teenage mistress , Elizabeth Blount , the only illegitimate offspring whom Henry acknowledged .
Simplified: Henry FitzRoy , 1st Duke of Richmond and Somerset ( 15 June 1519 â `` 23 July 1536 ) was the son of King Henry VIII of England and his teenage lover , Elizabeth Blount .