Secret BrucexClarkxLois AU I’ve been plagued by and I really want to write about one day.
Lois has a child but it’s not Clark’s. Bruce is their secret lover and despite the precautions taken, Lois ends up pregnant. Naturally they all think it’s Clark’s because Bruce always wore protection/had a vasectomy or whatever. Clark and Bruce are basically lookalikes so there’s no reason to think it’s not Clark’s when it’s born.
They are relieved but also worried when no powers manifest and the kid seems unaffected by kryptonite. When the kid reaches the same age Jon was when he started gaining his powers, Clark and Lois have Bruce scan to see if the child is going to develop them at all. This is when Bruce has to break the news that the kid has no Kryptonian genes at all. Now they have to grapple with the fact that this kid’s whole existence is different than what they thought and whether they should tell them or not.
For more angst: Bruce secretly ran the DNA right when the child was born and knew the whole time it was his, but he saw how happy Lois and Clark were with their baby and let them enjoy their family together.
For even more angst: The kid eventually finds out on their own that “uncle” Bruce is their actual dad and assumes the worst, thinking they’re an affair baby and if anyone found out, their family would fall apart.