It’s an animal owner’s worst nightmare: Being told that your pet needs to be put down.

Now imagine finding out that your vet, who promised to end their suffering, had actually given poor Fido away to a fellow employee — who then took him home and kept him for five months.

Well, that’s exactly what happened to Keri Levy, of Freehold Township, New Jersey.

The heartbroken dog owner and mother of two described the horrifying ordeal in a Facebook post this week, saying she had been tipped off by an anonymous resident.

Back in May, Levy had been forced to bring her beloved pooch, Ceaser, to a veterinary hospital in Howell due to a chronic health condition known as Cushing’s disease. It is one of the most common endocrine disorders found in canines and often leads to the process of euthanizing.

Thus was the case for Ceaser, Levy’s pet of 15 years.

The miniature pinscher was supposed to be put down, under orders from Levy’s vet, Dr. George Menez, formerly of Briarwood Veterinary. Workers even went so far as to call Levy to tell her that Ceasar was “at peace” following the purported procedure.

But Menez apparently let the poor pet live — and instead gave him to an employee who no longer works at Briarwood.

Levy said Monday that she recently learned the truth about Ceasar and went to the veterinary hospital to find out for herself.

“This has been such a cruel day,” she wrote on Facebook. “I arrived at the vet at 8am- Dr Menez was not here but the new owner was…I asked for cremation receipt – she didn’t know where anything was but was so helpful she called the cremation company Dr Menez was using. NO RECORDS OF MY DOG!”

Levy continued, “We called the police, SPCA…. police came… in the meantime Dr Menez called back the office and got on the phone with me – He ADMITTED that my Ceasar was Alive and that the girl in the office that used to work there had him in her possession….obviously there is a lot more to this conversation and I can not type it all. I am so rattled… we got the girl to bring the dog back to the vet.”

After being reunited with Ceasar, Levy was horrified to see how his health had deteriorated.

“Our dog is worse than he was,” she said. “No treatment for him, no medical care at all. He has lost 10lbs since May 17th… his bones are deteriorated- and his body is absorbing the muscle tissue. He smells from a skin condition. He is blind in one eye and almost the other has a large growth on it. He has several masses on his body… he suffered prior from Cushing-he hasn’t had any meds and most likely had/has some form of cancer. What game [sic] these people the right to do this!”

Levy told NJ.com that she spent about an hour with Ceaser before he was eventually put down — for real this time.

“After his check up today the new doctor said the right decision to stop his suffering is to be put to sleep,” she wrote on Facebook. “We now have to relive losing our little guy and have to explain the unexplainable to our children. Truly heartbreaking. Rip little buddy we love you and we are so sorry you had to suffer the last few months… xoxo.”

Speaking by phone Tuesday after Ceaser was euthanized, Levy said she was still shaken up.

“Awful, just awful,” she said. “Imagine having to tell a 9-year-old and a 10-year-old this. My 9-year-old was like, when can I see him?”

Attempts to reach Menez by NJ.com were said to have been unsuccessful.

A worker who answered the phone at Briarwood told the website that he had been “let go” over the weekend, but wouldn’t say why. It’s unclear if Levy plans to file a lawsuit against him.