Billy Joe Cobra is Spencer Father
You people said you would like to hear the theory, so here it is.
I think BJC is actually the father of Spencer. I give you some points.
They say they inherit the place, even if they say they are distant cousins (seem strange, because he don't seems to like Spencer's parents).
But Billy would have in his will that everything goes to his son.
And if he didn't do his will, beacuse he was young and didn't think of die, logically everything would go to his Son. (and parents, if he did not cut them off in his will)
An other thing is that Spencer could just call the Zoo, to ask if he could get Billy's Pet. He don't need to get his parents on the phone.
Same thing with the Plane Spencer is just allowed to use that thing.
Why didn't Spencer know? There are three options.
Spencer does know but don't want to freak Billy out beacuse, he seems to have forgotten it due his Dead. (he also forgot his pet until something reminded him of her)
According to the age of the Crocodile, Billy must be dead from 5-10 years. He also could have the Pet after he gives Spencer to his Cousin. So maybe Spencer has no idea and Billy don't want to tell him beacuse he don't know how, so he is just trying to make Spencer happy and spends time with him.
Both don't know, but Billy has this strong affection for Spencer. And starts hanging around, always. Billy forgot it and Spencer just never knew.
And than there are people who says that they are in love. We actually saw Billy kiss Spencer in the Show, but I don't think that that is the way a Casanova pop-star kisses people he's interested in.
Billy seems to has many lovers when he was alive. So Spencer could be the child of a fan. Either something happens to the mother or she just gave the child to BJC because something (she don't want it/she thought Billy would be a great Dad/she was not allowed to have the Child , or what ever).
We don't know what caused Billy's dead. But if it was Madame X his crazy stalker it would be possible that he was afraid something could happen to lil'Spencer. And so he gave him to his cousin until the problem was solved. But he died and could not take Spencer back.
Could also be that he gives the child away because he thought he would be a terrible dad. And so gives it to some relatives who he knew they would not go to the newspaper.
They have similar body shapes and eyebrows, eyes and ears, hair is also pretty similar. I know that many people say that the Charakter design in the show is questionable. But they seems to have some similarities.
But if we look at the Wright's Spencer don't really seems to have anything from them.
Jessica on the other hand, has the eyes of her father, eyebrows of the mother, mouthshape of her father. And I think mom's eye color could also be green in some pictures, but I'm not sure.
Also it's strange that they say they are distant cousins, is Billy not having closer family, to give his money?
Also the Wright's parents don't seem so interested in Spencer, there clear favorite is Jessica.