Due to the condition of Prince Rainier who has been in hospital since 7 March and was taken into intensive care a week ago the palace said Prince Albert would take over as his father was no longer able to exercise his royal functions.
Prince Rainier, who is being treated for heart, lung and kidney problems, came to the throne in 1949 and is one of Europe's longest reigning monarchs.
The health updates from doctors at the hospital this week have not been optimistic, with reports that the prognosis was pretty bad although his state is fragile
Prince Albert, 47, is the only son of Prince Rainier and his late wife, American actress Grace Kelly.
He is not married and has no children...which is a major source of concern in the country