Charles III is head of state of 15 Commonwealth realms and has had 16 prime ministers throughout his reign. Within the Westminster system in each realm, the King's government is headed by a prime minister. Appointment and dismissal of prime ministers are common reserve powers that can be exercised by the King or his governors-general. To date, Charles has appointed one new prime minister; Rishi Sunak as Prime Minister of the United Kingdom on 25 October 2022.