I don’t think Regina is Rumple’s daughter. Did Cora learn magic before or after she married Henry sr? Cora finds power very alluring, so it is possible that when she was younger and under Rumple’s teaching, Cora may have used her feminine wiles to try and get close to Rumple because he was the most powerful man in the land. The fact that Rumple swore not to love anybody else and considered himself a monster and unlovable suggests that he wouldn’t have gone so far as to sleep with Cora but may have enjoyed her attentions and even engaged in flirtatious games with her. He was trying to flirt with Regina in The Doctor when she was his apprentice then there was that other apprentice that he watched Regina kill. Rumple isn’t stupid, he knows that most women don’t want him but his power, hence why he had trouble believing that Belle could genuinely love him in Skin Deep. He would never let the likes of Cora get too close because he knows that she is only after power.
All magic comes with a price!
Keeper of Felix