Princess Leonor and Princess Sofia, daughters of the Crown Prince Felipe and Princess Letizia, sat patiently throughout the ceremony which saw King Juan Carlos leave the throne after nearly 30 years.
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King Juan Carlos and his granddaughters
The pair were wearing adorable dresses, Leonor in an ivory outfit and her hair tied back in a side braid, while Sofia wore a pale rose coloured dress with a headband.
It is rare that the two girls attend events. Their presence in early May at the General Air Academy was the first act they attended with their parents.
However, King Juan Carlos's abdication was a special moment, and the two girls will be at their father's coronation tomorrow as well.
At 10am Spanish time (9am GMT) on Thursday, the princesses will arrive from the Zarzuela Palace to Congress with their parents and sit alongside them on the platform where the prince will be crowned.
Queen Sofia kisses her granddaughter, while Prince Felipe, King Juan Carlos and Princess Letizia look on
Once the act is over, they will take part in the military parade and then head towards the Royal Palace. On the balcony, we will be able to see the daughters of the King, as they greet the Spanish crowds.
As her father becomes King, Princess Leonor will become the Princess of Asturias.
As heir to the Crown, she will receive the titles of Princess of Girona and Princess of Viana, corresponding to the firstborn of the Kingdoms of Castile, Aragon and Navarre, whose union in the sixteenth century formed the Spanish Monarchy.
She will also hold the titles of Duchess of Montblanc, Countess of Cervera and Lady of Balaguer.