Archanis IV

From Memory Alpha, the free Star Trek reference.

Archanis IV is the fourth planet in the Archanis system and one of the most important worlds in the Archanis sector. The planet was part of the Klingon Empire until the mid 23rd century when the Klingons ceded it to the United Federation of Planets.

Under the influence of the Beta XII-A entity, Pavel Chekov believed he had a brother, Piotr Chekov, who had been killed by the Klingons on Archanis. (TOS: "Day of the Dove")

Following the beginning of the Federation-Klingon War (2372-73), Gowron sent a message to the Federation Council, telling them to remove all Starfleet forces from the planet and the system. The planet was soon taken over by the Klingons. (DS9: "Broken Link", "Apocalypse Rising")