Having Rose McGowan as young Cora was pretty great casting. There were times I actually thought they were doing CGI to somehow de-age Barbara Hershey to her younger days in the flashbacks with how much of a resemblance there was.
BTW, if you want twisted... How about if Rumple and Cora had sex and Regina is actually Rumple's daughter?
That would make Henrys adoptive Mother also his Aunt.
Of course I'm thinking the answer there is no since the agreement they signed clearly would give the firstborn if it was his to Rumple so wouldn't he then know it?