From Halopedia, the Halo wiki
When the Covenant attacked Ariel, Charles was seated in the transmissions bay of the colony, and died from the shock of seeing the Covenant attack. Another civilian then pushed his body off the chair to send a distress signal to the UNSC. Later, a team of Orbital Drop Shock Troopers found his body. They noticed no signs of violent death, concluding that he had died of a fear-induced heart attack.
List of appearances