The Battle of Psi Serpentis was a major conflict between a UNSC fleet of 162 warships led by the UNSC Everest and Admiral Preston Cole and two fleets of Covenant warships totaling over 300 ships in the Psi Serpentis system in April 2543. The battle was a planned attack by Battle Group India on the Covenant fleets, and through a series of planned maneuvers, as well as the brief intervention of a suspected Insurrection fleet of 55 ships, the Covenant fleets were destroyed. After the first two waves of attacks, the battle culminated with the UNSC Everest leading the remaining Covenant vessels towards the systems gas giant, Viperidae. Getting the Covenant ships as close as possible to the planet, the Everest launched 100 nuclear missiles into the planet, causing the gas giant to very briefly ignite into a star, vaporizing the Everest and all the remaining Covenant ships.
While it has never been confirmed, it is suspected that Vice Admiral Cole was able to escape at the last second via slipspace and avoid death. Cole has not been heard or seen from again, though, so his survival is still legend.