MADRID (AP) — The heir to the Spanish throne, Princess Leonor, swore allegiance to her country's Constitution on her 18th birthday at a gala event on Tuesday that laid the groundwork for her eventual succession as queen when the time comes.

The nationally televised ceremony in the lower house of Parliament is understood to symbolize the continuity of Spain's parliamentary monarchy and the institution’s allegiance to the chamber.

Leonor de Borbón Ortiz used the same oath as her father did when he — then prince — turned 18 in 1986, pledging “to faithfully carry out my duties, to keep and uphold the Constitution and the laws and respect the rights of citizens and the autonomous communities and loyalty to the king.”

Leonor became crown princess when Felipe VI was proclaimed king on June 19, 2014. Her face has been in the media a lot lately and already the term “Leonormania” is being used, underlining her growing popularity as the modern face of the future monarchy.

Tuesday's ceremony was necessary for her to be able to succeed to the crown and someday become queen.

Banners with her photograph decorated lampposts along several of Madrid's main streets. Many official buildings were festooned with drapes and tapestries for the ceremony, broadcast on national TV and on several giant screens set up in the capital.

The royal family arrived at the parliament escorted a by a mounted squadron of the Royal Guard. Leonor and her younger sister waived from inside their Rolls Royce to the crowds lining the streets of central Madrid, which had started to gather from early in the morning.

Representatives from leftist political parties, including three government ministers, and lawmakers from Basque, Catalan and Galician regional and separatists parties boycotted the event as they favor a republic, not a monarchy.

The royal family is still trying to recover its former good name in Spanish society and make up for the scandals involving several family members, most notably former King Juan Carlos, Leonor’s grandfather.

Neither Juan Carlos nor former Queen Sofía attended the special parliamentary session or the subsequent ceremony later in Madrid's Royal Palace, but they were to be present at an evening family gathering in the Pardo Palace outside Madrid.

Juan Carlos, 85, who abdicated in 2014, left Spain for Abu Dhabi, the United Arab Emirates, in 2020 amid a cloud of financial scandals. Investigations of his finances in Spain and Switzerland have since been dropped while he won a separate lawsuit, against a former lover, in October.

He has made it known that he would like to return Spain but it’s not clear whether Felipe or the government would agree to that just yet.

Felipe and Letizia have recovered a lot of the institution's good image but for many in Spain the monarchy is still questioned, given that it was former dictator Gen. Francisco Franco who put Juan Carlos on the throne, bypassing his father and natural heir, Juan de Borbón. Spain had not had a royal family since Alfonso XIII went into exile with the coming of the Second Republic in 1931, five years before Franco and other generals staged a coup.

The royal family's popularity today is difficult to gauge. Spain's main polling body stopped asking Spaniards what they think of the royals in 2015 amid the myriad scandals.

Leonor has been groomed by her father and mother, who before marrying Felipe was a television journalist. She has shown regal aplomb when presiding over the awards ceremony of the Princess of Asturias Foundation and other honorific institutions that she heads.

She is currently receiving basic military training at an academy in the northeastern city of Zaragoza. She speaks English, French, Catalan, a language spoken in northeastern Spain, and some Arabic.

Little is known about Leonor’s personality as she has yet to give media interviews. But when she received her high school graduation diploma in Wales earlier this year, her fellow students cheered her on and her tutor praised her “unwavering passion for learning, for understanding people, and exploring diverse perspectives,” adding that they would miss her sense of humor.

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Associated Press writer Joseph Wilson in Barcelona, Spain contributed to this report.