A Tomboy to a Pregnant Princess - Bundled Series, #4

Piper is a 23 year old gal who works at a car shop, fixing engines and changing tires. Or she used to, at least. On her 23rd birthday, after her friends drop her off at her place, as soon as she locks the door, she blacks out. She wakes up in a palace, and gets told she is the heiress to a kingdom, bound to the land by a curse. Piper does not want to be bound to that place, much less to be a princess.
But the curse starts working at her body right away, making her more fit for being the face of the nation, and for continuing her royal bloodline. Between being stuffed into huge, poofy ball gowns, and trying (unsuccessfully) to keep her ever-blossoming bosom from popping out of said gowns, continuing ANY bloodline is the last nightmare scenario on Piper's mind. Everyone around her seems oblivious to her distress.
Everyone, except for a middle-aged history professor, who was supposed to be teaching her etiquette - a side gig he took, thinking the "Kingdom" was just an enclave for eccentrics and/or people whose ancestors lived there. The moment Piper first looks at him, she feels the carnal desire she had not previously experienced in her life. Being the confident and straightforward lass she is, she acts upon her feelings.
But whatever overtook her body, does not overtake her heart. And while her romantic feelings towards the professor remain non-existent, the middle-aged man appears to be growing more and more infatuated with her each time she seeks him out for his body. He keeps his feelings to himself, however, knowing how much of a burden a relationship with him could be for a woman so much younger than him, even in the most common circumstances. Breaking the curse by abdicating willfully is the only way to set herself and the people of the Kingdom free.
Piper plans on doing so on her coronation day, as soon as the crown touches her head. Unfortunately, there is more nuance to the curse, and all of her court assumes she knows it. Her confident pursuit of her own long-awaited urges might have perfectly natural consequences, sped-up and multiplied by the magic. As a result, she might be able to leave, but carrying more than just bizarre memories and unusually large feminine assets.