Help me identify this book!

I’m losing my mind trying to remember the title of this book. All my searches lead to weird places. The MMC is titled and has a young, rebellious ward (FMC) come and live with him and his sister, widow Pamela. Of course the MMC and FMC engage in scandal and get married. Pamela falls for a security guard who is guarding the estate because someone is trying to kill MMC. In a future book that security guard turns out to be royalty of a foreign nation. Can anyone make sense of this narrative and offer a title and author? Thanks!