According to Jim (2001)

S5E19 Daddy Dearest

Jim comes to the startling conclusion that Bill, who is the father of one of Ruby and Gracie's classmates, might actually be his biological father who left him as a child. As Jim grapples with this revelation, he embarks on a quest to uncover the truth about his past and the identity of his father, leading to significant emotional turmoil and unexpected confrontations.