Mum-to-be Kayley Bettany was visiting Colchester Zoo with her husband Kieran when they visited the orangutan enclosure.
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After revealing her bump to Rajang, an orangutan, he pressed his large face up against the glass to get a closer look. He then tried to tenderly touch her through a glass barrier.
The amazing clip was filmed in January at Colchester Zoo in Essex.
Ms Bettany can be heard in the video saying: "He's trying to hold it. That's so cute, isn't it".
The orangutan then appears to press his ear against the glass to listen to the baby before again trying to kiss her tummy.
"This was a wonderful experience however upsetting at the same time. He even had a tear run down his face", Kieran said.
The video has already been viewed nearly 20 million times.