Proud parents! Queen Letizia and King Felipe of Spain watch as Princess Leonor, 17, takes part in a flag swearing-in ceremony at the General Military Academy

Queen Letizia and King Felipe of Spain looked on as proud parents as they watched Princess Leonor attend her flag ceremony today.

Their 17-year-old daughter, heir to the Spanish throne and Princess of Asturias, looked regal in military uniform as she stood in formation alongside her fellow cadets.

The ceremony at the Zaragoza Military Academy was presided over by her father King Felipe, 55, who was joined by Queen Letizia, 51.

While the monarch wore his military uniform, his wife opted for a blue and black sleeveless polka dot dress, which featured bottom detailing and a cinched waist.

According to tradition, the ceremony saw Leonor kiss the Spanish flag after swearing allegiance to her king.

Queen Letizia and King Felipe of Spain looked hand in hand with the proud parents as they watched Princess Leonor attend her flag ceremony today.

Leonor looked regal in military uniform as she stood in formation alongside her fellow cadets. Pictured right: According to tradition, the ceremony saw Leonor kiss the Spanish flag after swearing allegiance to her king

After the Spanish national anthem was played, King Felipe reviewed the troops, walking in front of his daughter.

The princess, who will be 18 later this month, had spent the week rehearsing for four hours a day. local media reported.

Her sister, Infanta Sofía of Spain, 16, was notably absent from today’s event because she is studying at UWC Atlantic College in the Welsh county of Vale of Glamorgan.

The school is often referred to as ‘Hippie Hogwarts’ thanks to its progressive approach to education and picturesque castle surroundings.

Leonor’s General Military Academy in Zaragoza, meanwhile, follows a strict schedule during the week, but the princess is free to return home at weekends if she is not on maneuvers.

After the Spanish national anthem was played, King Felipe reviewed the troops, walking in front of his daughter

The princess, who will be 18 later this month, had spent the week rehearsing for four hours a day.

The ceremony at the Zaragoza Military Academy was presided over by her father King Felipe, 55, who was joined by Queen Letizia, 51.

Princess Leonor of Spain swears in the Spanish flag during an official ceremony

After training at the General Military Academy in Zaragoza, which is Spain’s equivalent of Sandhurst, she will go to naval school and complete her three years at the General Air Academy.

The princess revealed her excitement about being a cadet at the Princesa de Girona Foundation awards ceremony in Girona, Catalonia, on July 5.

She said: “I have just finished high school and I am about to start a new phase with a period of military training.

“I’m happy because I know how much the Spanish appreciate our armed forces… it’s an important moment in my life and I feel very excited and determined to keep learning and give my best.”