“Lucky Charm Secure”

I have looked through posts trying to find a book that has a gut punch moment like the moment in the movie First Daughter where Samantha realizes that James is actually a part of the Secret Service and not just a normal guy who was interested in her.

I have NO issue with age gap. Only want one love interest - M/F.

Main thing I am looking for is a FMC who does not realize the true identity of the MMC and it is a gut punch when she realizes who he really is. Bonus if everyone else knows and she is the only one who doesn’t realize his true identity.