Joe Exotic's husband Dillon Passage has said that he has been left 'heartbroken' after reading the Tiger King star's disturbing three-page letter that was released over the weekend.

In the note, penned from his prison cell, the 57-year-old hit out at his alleged poor treatment behind bars, predicting that he will be "dead in 2-3 months".

Exotic also criticised Passage, accusing him of breaking off contact and revealing that seeing pictures of him enjoying his new-found fame on social media left him feeling "dumped like a dog in a shelter".

Replying via Instagram, 22-year-old Passage wrote: "My heart is breaking after reading Joe's letter. He is living in hell right now and I'm outraged by the way he is being treated. I can't even begin to imagine how that is breaking his spirit.

"I love Joe and I'm standing by him. The photos that I post on here are a highlight reel of my life... What you don't see are the hours that I'm alone at home, missing my husband and my friend.

"I've been writing letters and it is a shame to hear that he isn't receiving them... I know they limit the amount he can read in a week and I only hope they eventually get to him.

"Joe, I hope that this reaches you too. Know that I love you and I'm fighting for you everyday. #freejoeexotic"

Exotic's legal team are continuing to petition Donald Trump to grant the former zookeeper a presidential pardon and secure his release from jail.