The angels have fallen. Castiel lost his grace, and is now a human. He experiences hunger, cold, need, but still pondered at the thought of love. Dean takes him under his wing and helps him understand his new way of life; every aspect. Even though his grace is lost, the affair between a man and an angel is forbidden. Not to mention, an angel and a Winchester. In addition to the internal conflicts between the two, they also have to worry about the bounty put on Castiel's head by the other fallen angels.

When Brimsley gets the job to be the queen's man, he is overjoyed at the excitement of working at living at the Palace. It is everything he dreamed of: the palace itself, his job, and someone he meets. The writers of Queen Charlotte/Bridgerton probably will not come up with a back story for Brimsley and Reynolds so this is my interpretation of how they came to be.