The Priest presented the bride and the groom with a ceremonial dagger and said, "You may now seal your marriage." He held a goblet in front of them and said, "Make a cut in your palm and drip your blood in this goblet. It will signify that you two are one from today onwards."
The goblet had a replica magic potion that would connect the two souls and bond them together. It was a way to validate the marriage of the Royals.
This particular marriage tradition was borrowed by the succubus from the King's memory of his actual marriage with Auvera. This was the tradition specifically followed by the Royals of Wyverndale.
The King had married all of his wives in their own Kingdom, following their own tradition. The concubines were also sent to the King by following their own tradition.
