Ceti Alpha VI

Ceti Alpha VI was the sixth planet in the Ceti Alpha system. The planet exploded some time in late 2267 or early 2268, approximately six months after Khan Noonien Singh and his followers were stranded on Ceti Alpha V. The shock of the planet's explosion shifted the orbit of Ceti Alpha V and laid most of the planet waste. (Star Trek II: The Wrath of Khan)