Watch Moving Tribute from 'Koko' the Gorilla to Robin Williams

Before Koko the gorilla cried over Robin Williams’ death, she laughed with the Oscar-winning comedic genius who died Monday at the age of 63.

The famous gorilla, who lifted what is only a whisper of a veil between human and non-human primates when she used American Sign Language to express her thoughts, first met Williams in 2001 when Woodside-based The Gorilla Foundation arranged for a meeting.

“We had no idea what to expect, but everyone was in for a treat, and they became special friends,” the gorilla conservation web site reports.

Here’s some background on the below video, as provided by The Gorilla Foundation:

In 2001, Williams was invited to meet Koko, the gorilla who can communicate a full range of emotion through sign language. Although no one knew what to anticipate, the two became special friends.

In the video, Williams frequently made Koko smile — something she hadn’t done for more than six months after her lifelong gorilla companion, Michael, passed away at the age of 27. Not only did Williams cheer up Koko, but Williams similarly seemed transformed — from a high-energy entertainer, into a mellow, sensitive, empathetic guy, who also happened to be really funny.

The two laughed like a pair of old pals, their mutual delight obvious in several side-splitting minutes of video used in a public service announcement to promote The Gorilla Foundation’s conservation mission.

Like most individuals privileged enough to engage in meaningful two-way conversations with a great ape who understands spoken English, Williams described it as “mind-altering,” “awesome” and “unforgettable.”

It was life-changing for the gorilla as well.

When the two met, Koko hadn’t smiled in the nearly seven months since the death of her lifelong gorilla companion, Michael, at the age of 27.

“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 Gorilla 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.”

When scientists Penny Patterson and Ron Cohn told Koko of Williams’ death Monday, was quiet and thoughtful, then later signed to Patterson, “CRY LIP,” The Gorilla Foundation said. LIP is the sign Koko uses for woman.

Koko responds to the news of Robin’s passing

Koko looks somber after it sinks in

(Images and video courtesy of the Gorilla Foundation.)