A student was elated to be given a "free puppy" - only to discover that the uncharacteristically wild dog was in fact a wolf.
He came across the creature after spotting a sign on a house in Tuscon, Arizona, offering the animal free-of-charge and decided to take him home.
But the "puppy", called Neo, proved to be unusually nervous, would defecate in his owner's car and would frequently escape to the neighbour's house, reported The Dodo.
As his owner was a full-time college student and had a full-time job, Neo spent extended periods of time in the backyard - from which he would often dig under or jump over the fence to play with the dogs next-door.
"He built a higher fence to help contain him, but Neo chewed through it and continued to escape," Cate Salansky of Wolf Connection told the animal website.
He avoided eye contact with them and would hide in the bathroom and did not show interest in dog treats.Despite being initially welcoming and allowing the wild animal into their house, the neighbours became increasingly suspicious of Neo's behaviour.
Eventually, they decided to take him to the Humane Society of Southern Arizona who told them that the creature was not a normal dog.
Neo not only looked like a wolf but also demonstrated the behaviour of the non-domesticated animal. Pictures show him pulling at the leash, not making eye contact with humans and behaving like a pack animal.
The organisation's former CEO Maureen O'Nell said she told them: "You know that isn't a dog, right?"
The couple told her that they had been "wondering".
She contacted Wolf Connection to ask whether they would take him in and after they agreed she spoke to his owner about whether he would be willing to give him up to the sanctuary.
When he agreed, Maureen said she was "proud of his decision," adding: "His boy had a wonderful life ahead of him at Wolf Connection."
The sanctuary put Neo in isolation when he arrived but they said he quickly escaped to find their alpha female Maya and on his first night joined the "nightly howl".
A video shows him energetically playing at the sanctuary with another wolf, Nova, when he arrived there nearly two years ago.