In a monarchy, a regent is a person appointed to govern a state pro tempore because the monarch is a minor, absent, incapacitated or unable to discharge the powers and duties of the monarchy, or the throne is vacant and the new monarch has not yet been determined. One variation is in the Monarchy of Liechtenstein, where a competent monarch may choose to assign regency to their of-age heir, handing over the majority of their responsibilities to prepare the heir for future succession. The rule of a regent or regents is called a regency. A regent or regency council may be formed ad hoc or in accordance with a constitutional rule. Regent is sometimes a formal title granted to a monarch's most trusted advisor or personal assistant. If the regent is holding their position due to their position in the line of succession, the compound term prince regent is often used; if the regent of a minor is their mother, and she is wife or widow of the king, she would be referred to as queen regent.