Koko: The Gorilla Who Talks To People is a documentary exploring the story of the only "talking" gorilla in the world and her relationship with animal psychologist Penny Patterson.
Project Koko began as a PhD project to teach sign language to a baby gorilla, but Koko and Penny have now been together for more than 40 years.
Koko's extraordinary life with Penny prompted a good deal of reaction on Twitter, with viewers sharing their thoughts on this remarkable programme.
Viewers were mostly amazing by the incredible intelligence of Koko.
But equally, they felt uneasy about a gorilla being kept in captivity. The programme highlighted how Koko not having children had deeply affected her.