Princess Leonor and Infanta Sofia marked a new milestone on Wednesday, carrying out their first joint outing without their parents, King Felipe and Queen Letizia.
The princesses planted trees in the protected forest area of Hayedo de Montejo in Madrid, along with a group of other teenagers, aged between 14 and 16.
The royal sisters participated in the European initiative, "A tree for Europe" to raise awareness about the fight against climate change.
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WATCH: Princess Leonor and Infanta Sofia's first joint outing without King Felipe and Queen Letizia
Princess Leonor, 15, and Infanta Sofia, 14, were both dressed casually in white T-shirts and jeans for their outdoor engagement, and donned face masks.
Meanwhile, their father, King Felipe, visited the school of navy officers in Cadiz.
The princesses helped to plant trees
It comes after heir to the Spanish throne, Princess Leonor, carried out her very first solo engagement in March, visiting the Cervantes Institute in Madrid as part of its 30th anniversary celebrations.
The princess is set for a big change this summer as she's set to move to the UK for the next stage of her education in August.
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It marked a milestone day for Princess Leonor and Infanta Sofia
Princess Leonor will study the International Baccalaureate program for two years at the UWC Atlantic College in the Vale of Glamorgan, Wales.
She will also be joined at the school this summer by another European royal – Princess Alexia of the Netherlands, who is the second daughter of King Willem-Alexander and Queen Maxima.
UWC is set in the 12th century St Donat's Castle on the southern Welsh coast and campus facilities include a library, woodland, an indoor and outdoor swimming pool, and classrooms within historic buildings.
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