Joseph-
He was not a Kohein, nor was he divorced. He only said it to be excused from dating her.
I did not believe the story at first until he said who the Shadchan was.
22OldGold-
There was a story about 8 – 10 years ago about a step- brother and step- sister (I think from Monsey) who married each other, but I don’t think there was a shadchan involved.