Twin Black Dragons

Voaraghamanthar and his broth 1] Waervaerendor, nicknamed by himself the Rapacious Raider.
After wandering Faerun for a time, they finally found a home in the Mere of Dead Men, attracted by the isolation of the place and legends about the hoard of Chardansearavitriol and the treasures of flooded Uthtower and other realms. They especially hoped to find the lost Twin Crowns of Myrmoran, reputed to have enhanced the empathic bond between the fraternal monarchs of Uthtower and Yarlith and granted them magical powers.
They started posing as only one dragon, named Voaraghamanthar, and soon tales were told across the Realms about the legendary Wyrm of the Mere, a strange black dragon that could appear out of nowhere to assault adventurers.
Despite not being really interested in becoming dracoliches, they approached the local Cult of the Dragon cell to use them for their plans. Thanks to the cultists, the Black Brothers recovered one of the Twin Crowns of Myrmoran.
The crown was given to a dragon, Voaraghamanthar, in exchange for his assistance in finding the lost Uthtower and the temple therein that was rumored to contain the remains of the dracolich Chardansearavitrio
https://forgottenrealms.fandom.com/wiki/Twin_Crowns_of_Myrmoran