Prince William begins life as an Army officer on Monday morning, as he's reporting for duty with his regiment.
Wills has joined the Blues and Royals regiment, based in Windsor. While he's there, he'll live with other officers in something called a barracks.
The 24-year-old royal is following in the footsteps of his younger brother Harry, who's also an officer.
William will learn how to lead troops in armoured vehicles, which are used to find enemy soldiers.
He'll spend a few weeks getting to know the people in his regiment before heading off to a five-month training course.
Eventually, he'll be in charge of about 12 soldiers in four Scimitar vehicles.