Second Chance Prince by Sara Bennett

The third exciting romance in a sweeping Regency series from bestselling author Sara Bennett follows a dashing Prince and his former crush as they pretend to be engaged to hide from a deadly threat—perfect for fans of USA Today bestsellers Evie Dunmore and Manda Collins!
Prince Nikolai of Holtswig has journeyed to London with one purpose: stay out of trouble until the unrest in his country dies down. But after an assassination attempt at the season’s first ball, he has no choice but to accept a deal from the British government. They will offer him protection … if he gets engaged to a proper Englishwoman. Niki isn’t interested—until they suggest his childhood friend, Lady Roberta Ashton.
Lady Roberta couldn’t help being a bit infatuated with Niki in the summers they spent together all those years ago. Faking an engagement would definitely liven up the season—but there’s a difference between lively and deadly. As the threats increase along with their attraction, Roberta and Niki must learn to trust each other to protect themselves—and their hearts.