From Paragon Wiki
King Mihenra, a self-proclaimed warlord from the Netherworld, attempted to seize control of Paragon City, only to be defeated by Positron on this very spot.
The Regal Badge is located in the Powderkeg neighborhood of Boomtown. It is one of the trickiest exploration badges to find in the game. 600 yards due west of the Powderkeg marker, there is a road. Directly north of that location, one level down, is a tunnel entrance. The badge marker is located in the middle of that tunnel along the center divider, 682 yards west of the Powderkeg marker.
Its coordinates are (-448, 42, 2170).