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WOODSIDE, Calif. (PIX11) — Robin Williams’ human fans aren’t the only ones saddened by the actor’s death.

Koko, a gorilla who communicates in American Sign Language and met Williams 13 years ago at The Gorilla Foundation in Northern California, also took the news pretty hard.

The Gorilla Foundation — which was founded in 1976 to expand on Project Koko, which studies the linguistic capabilities of gorillas — invited Williams to meet with Koko in 2001.

When foundation co-founder Dr. Penny Patterson told Koko that Williams had died, she was “quiet and looked very thoughtful,” according to a statement from the foundation Tuesday.

“More phone calls about the news came in, and Koko overheard one from a former colleague who had worked with Williams while he filmed a public service announcement for The Gorilla Foundation (based on his visit with Koko) in 2003,” Patterson said. “The colleague’s voice broke at the end of the conversation.  About a half an hour later, Koko signed to Penny:  “CRY LIP” (LIP is Koko’s sign for woman).

“At the end of the day, Koko became very somber, with her head bowed and her lip quivering.”

(Photo: The Gorilla Foundation)

The foundation honored Williams’ life by sharing the video of his “powerfully emotional meeting” with Koko in 2001:

Staff at the foundation say that Williams made Koko smile for the first time in six months, since her gorilla companion, Michael, died at the age of 27.

They said that not only did Robin cheer up Koko, but Robin seemed to transform “from a high-energy entertainer, into a mellow, sensitive, empathetic guy, who also happened to be really funny.”

“Koko and Robin’s encounter is a supreme example of how humans and gorillas can overcome interspecies boundaries and express the highest form of empathy — embracing differences,” the foundation said.

“Robin’s ability to just ‘hang out’ with Koko, a gorilla, and in minutes become one of her closest friends, was extraordinary and unforgettable for Koko. We hope that it now becomes unforgettable for you too.”