Fans of Eloisa James & Julia Quinn discussion

Years ago I read a book by Julia Quinn about a girl who was illegitimate and who went to a ball Cinderella styel and met a lord and really connected. Later, he spent years looking for her only to discover that she was socially beneath him. Anyone know the name of the book?

Benedict and Sophie :)

I think it's an offer from a Gentleman? I love Sophie!