Talk:Xavier and Fred Johnson/@comment-30265419-20161018234828

What I thought when I saw this episode was, that fred is actually Ferb's son, because he has brown hair just like Ferb's father and grandfather. Additionally, even though we don't know who Ferb married, Vanessa Doofenshmirtz is definetely a love interest, and she is a brunette, so maybe Fred is their son.

So Xavier and Fred are cousins, which explains why they hang out together, and also Candace only showed interest in having two kids in her life several times before, so why would there suddenly be three.

That might be a fan theory that doesn't hold up, but the possibility is still not excluded.