Not only is Joe Hill a new character on Blue Bloods, but he’s a new grandson to the Reagan family. There were a couple storylines converging that led to the discovery of Joe Hill as a new member of the Reagan family. Not only did his cousin, Sean, discover he had a long-lost cousin, but Paula, Joe’s mom, tries to convince Frank Reagan to put Joe on a less dangerous case. She finally reveals that he is Frank’s grandson to try to sway him.

The reason no one knows Joe Hill is related to Frank before this is because their relation is through Joe’s deceased father, Joe Reagan. Joe Reagan’s girlfriend, Paula, was pregnant when Joe Reagan died by the hands of corrupt cops. Paula kept her son, Joe, from the Reagans, and hid his cop legacy; however, Joe decided to become a cop anyway, carrying on the family legacy.