Original: In some monarchies, such as the United Kingdom, an interregnum is usually avoided due to a rule described as "The King is dead. Long live the King", i.e. the heir to the throne becomes a new monarch immediately on his predecessor's death or abdication.
Simplified: In some monarchies, such as the United Kingdom, an interregnum is usually avoided due to a rule described as "the king is dead, long live the King", i.e. the heir to the throne becomes a new monarch immediately on his predecessor's death or abdication.