Some fan theories can really be interesting while some others seem to be an out-right stretch. One of the latest running around is the idea that Holden Radcliffe (John Hannah) on Marvel's Agents of SHIELD is actually Leo Fitz's (Iain De Caestecker) father. EW.com went straight to the source and asked executive producer Jed Whedon:
They're both Scottish, and we've discussed it at length. Truthfully, there's no one better to play his dad than John Hannah, but no, Radcliffe is not his father.
I'm not sure how this theory ever got started. Every indication is that Fitz knows who his father is and has a bad history with him. Radcliffe has admitted to knowing Fitz's father, but I can't see how the logic jump happens to get to them being related… or even why.