Well, at least after watching 3×14 we can safely rule out Rumple being the father of Zelena. She needed a drop of Rumple’s blood to open his safe which had been sealed by blood magic. If she were really his daughter, she could have opened it herself, similar to how Neal was able to open his father’s hidden cabinet in the Dark Castle in 3×3. There you go. Concrete proof that Zelena is not Rumple’s daughter.
Praise the lord
Zelena did give a few hints about her father though. He was a drunk who couldn’t hold his hands steady enough to hold a razor blade, so Zelena had to shave him herself.
personally I think that rules out Leo as well
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"He was a lot of things to me" "The only conclusion was love"