Warning: Article contains descriptions of sex abuse of animals.

The heart wrenching story of an orangutan that was used as a sex slave in Indonesia has re-surfaced after conservationists who rescued her revealed details about her painful recovery.

Pony, an endangered Borneo orangutan was rescued from an Indonesian brothel in 2003, after being found chained to a wall, and prostituted to local men for sex.

Taken away from her mother since baby, Pony's captors taught her to perform sexual acts and forced her to wear make-up and jewellery.

Director of the Borneo Orangutan Survival Foundation, Michelle Desilets told VICE that Pony's owners were very reluctant to let her go.

"She was being used as a sex slave. She was probably about six or seven years old when we rescued her, but she had been held captive by a madam for a long time."

In the end it took 35 policemen armed with AK-47s and other weaponry going in there and demanding that they hand over Pony.

Her captors threatened the rescue team with guns and poisoned knives as they believed Pony brought luck and fortune to the family.

After 15 years, under the care of a group of conservationists, Pony has managed to fully recover from the horrific ordeal and learned to trust humans again.

Her carers spoke out about Pony to raise awareness about the treatment of orangutans, particularly the loss of their habitat due to palm oil plantations.

Lone Droscher-Nielson, who was part of the team who rescued Pony in 2003, told the Sun, "The first baby steps were to make her trust us in her new home."

"We tried to keep men away from her enclosure as she was afraid of them".

"She slowly recovered and male carers were slowly introduced to her. She didn't seem to be afraid of them anymore and she was happy with any company she could have", Ms Nielson added.

Pony now lives with seven other orangutans at the Nyaru Menteng Rehabilitation Centre, but unfortunately cannot be released into the wild due to her poor survival skills.

Since her rescue, Ms Desilets described Pony's resilience as 'amazing', saying that she had the best personality and learned to trust humans very quickly despite her sad ordeal.