Simplify the following text for a Grade 8 native English-speaking person.
Original: AgnÃ s Sorel ( 1421 -- 9 February 1450 ) , known by the sobriquet Dame de beautÃ , was a favorite mistress of King Charles VII of France , to whom she bore three daughters .
Simplified: AgnÃ s Sorel ( 1421 -- 9 February 1450 ) , was a favorite mistress of King Charles VII of France .