She was 33 years old.
A spokesperson for the palace issued a statement last night, saying the queen is "shocked and devastated" at her sister's death and immediately flew to Argentina with her husband, Prince Willem-Alexander.
Queen Maxima of Holland's youngest sister, Inés Zorreguieta, was found dead in Argentina in an apparent suicide, local media reported.
Ines Zorreguieta, 33, the younger sister of Queen Maxima of the Netherlands was found dead in her apartment in Buenos Aires, Argentina.
Understandably, the Queen is shocked and very upset.
Zorreguieta appears to have committed suicide, the Dutch embassy in Argentina told Euronews in an email. It is intensely sad and heartbreaking news that can hardly be comprehended for those who stay behind. Our thoughts and prayers are with the Queen and her family.
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Ms Zorreguieta worked for the Argentine government as an official in the Ministry of Social Development. I wish them all the strength necessary to carry this terrible loss together.
Queen Maxima, 47, has two other brothers, Martin and Juan, and three half-siblings, the BBC reported. Zorreguieta is believed to have taken her own life.
She has cancelled upcoming engagements over the coming weeks, including a Baltic tour to Lithuania, Estonia and Latvia with her husband next week.
Inés and Maxima's father, Jorge Zorreguieta, passed away in August 2017 after years of ill health.
Buenos Aires-born Maxima had a close relationship with her youngest sister, who was bridesmaid at her wedding to then Crown Prince Willem-Alexander in 2002.