Because of Miss Bridgerton : Book 1 by Julia Quinn

A generation before the Bridgertons, there were the Rokesbys...
 
Everyone expects Billie Bridgerton to marry one of the Rokesby brothers, and she's not opposed : their familes have been neighbours for centuries. There is only one Roseby Billie absolutely cannot tolerate : George. He may be the eldest, and heir to the earldom, but he's arrogant, annoying and she's certain he detests her. Which is perfectly convenient, as she can't stand the sight of him either. 
 
But when Billie and George are quite literally thrown together, a whole new sort of sparks begin to fly. And when these lifelong adversaries finally kiss, they just might discover that the one person they can't abide is the one person they can'y live without...