Schooled By the Bastard by Annabelle Anders

Second Chance * Secret Past * Bastard Hero

In this second chance Regency Romance by Annabelle Anders, an independent headmistress fights to keep her all-girls school open even as the only man she’s ever loved—and lost—barges back into her life.
As the daughter of a cruel marquess, Augusta Primm has fought tooth and nail to establish her independence. But now, with someone vandalizing her precious institution, and scandals turning up left and right, the school’s reputation hangs by a thread. Slowly but surely, she’s losing the fight.
Rowan Stewart, older brother to the Duke of Bedwell, is a bastard by birth, and an architect by trade. Despite his brother’s push for him to enter society, Rowan will never be subject to society’s prejudice again. Once was enough.
Until a once in a lifetime project comes along—the opportunity to rebuild the majestic Longbow Castle. It doesn’t matter that the castle is just a few miles from the school owned and run by the woman who jilted him years ago. He’s left that life behind and he’d never allow Augustine Primm to hurt him again.

But when she faces losing the dream she chose over him, Rowan must make a choice. Help the woman he once loved or abandon her forever.
The choice should be simple but with Augusta Primm, it’ll always be complicated.