The Denver Zoo posted a heartbreaking message to their Facebook page Monday (Dec 21): Nias, the matriarch of their Sumatran orangutan family, has died.

Nias passed unexpectedly on December 17. Her care team at the zoo are awaiting the results of her necropsy from Colorado State University’s College of Veterinary Medicine & Biomedical Services to find out the cause of her death.

In their tribute post, the zoo says that Nias was seen as the "queen bee" of the Great Apes exhibit, and was also a mother of two. She was also a "wonderful mate" to Berani, her offspring's father, who I'm sure will miss her greatly. Read the Denver Zoo's full post about Nias right here and try not to cry:

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Animals of the Denver Zoo