Romancing Mister Bridgerton: Julia Quinn

Penelope Featherington has secretly adored her best friend's brother for... well, it feels like forever. After half a lifetime of watching Colin Bridgerton from afar, she thinks she knows everything about him, until she stumbles across his deepest secret... and fears she doesn't know him at all.
Colin Bridgerton is tired of being thought of as nothing but an empty-headed charmer, tired of the notorious gossip columnist Lady Whistledown, who can't seem to publish an edition without mentioning him. But when Colin returns to London from a trip abroad, he discovers nothing in his life is quite the same-especially Penelope Featherington! The girl who was always simply there is suddenly the girl haunting his dreams. When he discovers that Penelope has secrets of her own, this elusive bachelor must decide... is she his biggest threat- or his promise of a happy ending.