Colonel Beauregard was the fiance of Magnolia. He lived long ago and is now deceased.
Magnolia was going to marry Beauregard on the Delta Queen, but she left him at the altar when she thought he had stolen her emerald necklace. In fact, the necklace was stolen by the captain of the Delta Queen, a rival for her affection, and hidden in the steering wheel of his ship in order to ruin the wedding.
The New Scooby-Doo Mysteries
His real ghost appeared after he was posthumously cleared, able to be reunited with the ghost of his love at last.