Dutch Queen Maxima paid an emotional tribute to her younger sister Ines who died at the age of 33 reportedly after suffering depression (Photo: AFP)

Dutch Queen Maxima on Tuesday paid an emotional tribute to her beloved younger sister, who was found dead after reportedly suffering from depression and mental illness.

In a rare public and personal speech, the queen thanked all those who have sent letters and messages following the death earlier this month of her 33-year-old sister, Ines Zorreguieta.

"My little, darling, talented sister Ines was sick. She couldn't find joy in anything and she couldn't get better," Maxima said as she visited a proton therapy centre in Groningen for treating illnesses such as cancer.

"Our only comfort is that she is finally at peace."

The queen added the "countless letters" she had received had been a real help and thanked everyone "for the respect that people have shown my family during this very tough time."

Maxima, who is originally from Argentina, flew to Buenos Aires with her husband Dutch King Willem-Alexander and their three daughters to attend a private funeral earlier this month.

Despite moving to the Netherlands, Maxima had maintained a close relationship with her sister, 13 years her junior. Ines was the maid of honour at Maxima's wedding as well as a godmother to her youngest daughter, Princess Ariane.