He later realizes she is also his biological daughter, having had a prior affair with Mariana's mother.
However, in an attempt to prevent his grandfather's death, Fry locks him in a cabin out in the middle of nowhere — which unknown to him is a nuclear test zone — resulting in his grandfather's death.
In season 5, Joy goes to meet a cousin she has not seen in years and instantly becomes attracted to him, prompting her to overlook the "taboo" nature of her crush and even considers dating him and having his kids, much to her roommates' disgust.