From Dragon Quest Wiki

Regan (Reed in the NES version) is a minor character from Dragon Quest IV: Chapters of the Chosen. He is the Prince of Ballymoral.

In Chapter 3, Torneko Taloon learns that Regan and Veronica, the Princess of Endor, are in love and wish to marry. Seeing Torneko's presence as an opportunity, Regan uses the merchant as a go-between to relay his letters to the princess and thus secretly apprising her father of King Shamus of Ballymoral's awful aspirations. Acting quickly, King Norman of Endor writes up another message for Torneko to transport, this time directed at his rival. The message explains to Shamus that the prince and princess are in love, and the realizes that through marriage his son will be the next king of Endor anyway, calling off the war plans.

The marriage of Prince Regan and Princess Veronica, takes place in the Endor colosseum, and continues through the entirety of Chapter 5 and 6.