An unexpected mourner deals with Robin Williams death

Stars and fans have all posted their heartbreaking responses to the death of Robin Williams.  But one of the actor's dearest friends, one who many may have thought could not comprehend what his death means, is now mourning the loss.

>>Photos: Remembering Robin Williams

Koko, the famous sign-language-using gorilla, has become somber since news of his death came into The Gorilla Foundation in northern California, according to the foundation's website,

At first, Dr. Penny Patterson said that Koko came with an "inquiring look" and then she explained to the gorilla that Williams had died.

As more calls came in, Koko, Patterson said, signed to her "CRY LIP" (lip is Koko's "word" for woman).

By the end of the day, Koko held her head bowed and her lip was quivering.

In 2001, Williams met Koko after her lifelong gorilla companion died.  She had not smiled in over 6 months, until Williams came in.  Officials with the foundation said that not only did Koko cheer up, but she had transformed him from his usual manic self to a "mellow, sensitive, empathetic guy."

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