An abandoned pup was on death row at the Brooklyn pound despite three willing foster families ready to rescue him — but he narrowly escaped euthanasia at the eleventh hour when The Post started asking questions.

Blue, a two-year-old mutt, was living as a guard dog on Staten Island but was relegated to a cold shed outside when a resident in the home became uncomfortable with his presence around her children, internal notes from the New York City Animal Care Center show.

After a week in the shed, the NYPD picked Blue up on Oct. 23 to bring him to the Staten Island pound. He was then transferred to the Brooklyn ACC location on Saturday after the Staten Island shelter was evacuated because of “unsafe” temperature conditions.

Blue was nearly killed but ended up in the loving home of a new foster parent.

Advocates were concerned the evacuees would be placed on ACC’s nightly “kill list” to be euthanized because of overcrowding — and sure enough, Blue, who had no bite history, was marked for death on the same day he was evacuated, emails show.

ACC staff sent an email Saturday to their New Hope partners — a coalition of rescue groups that take in dogs that aren’t yet ready for a direct adoption because of behavior or health issues — saying Blue and a few other pups would need to be pulled by 12 p.m. Tuesday to avoid euthanasia.

A rescue group wrote to ACC on Tuesday begging for more time, saying they had willing fosters but they needed another day to vet the applications, which had references that weren’t picking up the phone, emails show.

ACC staff wrote back that the deadline couldn’t be extended past 5 p.m. and there was nothing they could do.

“The New Hope department was just adamant, ‘no it wasn’t happening, no he’s not being given more time,’” said a rescue volunteer who asked to remain anonymous to avoid reprisal from ACC.

When advocates called the New Hope department at ACC, staff insisted the dog was dangerous and had “triggers” because he once lunged at a handler a few days into his stay, according to numerous people on the call and internal ACC notes.

The Post became aware of the situation around 5:30 p.m. Tuesday and, assuming the pup was already dead, reached out to ACC’s spokesperson to ask why the dog was euthanized when there were fosters at the ready.

About 40 minutes later, the spokesperson responded saying only “Blue has not been euthanized.”

Shortly after that, the New Hope department emailed the rescue group with instructions on how to process the foster’s applications.

“They suddenly changed their mind and gave him until the next day,” the rescue volunteer said.

ACC didn’t respond to an additional request for comment Friday.

By Thursday, Blue was free and ecstatic to be living with his new foster mom Sophie Anthony in Hoboken, New Jersey.

“It broke my heart,” Anthony, 24, told The Post of the experience trying to rescue Blue.

“I think that everyone, including dogs, are capable of change. It’s really a result of their environment and things like being in a shelter can really amplify scared or negative behavior and I don’t think it’s fair,” the account manager continued.

“With the opportunity to save [a dog] that was literally going to be killed, I felt I had to do everything in my power to make sure that he wasn’t.”

When Blue first arrived at his new foster home, he was “a little hesitant” to come out of his crate but within two hours, he was “rolling on his back” and “kissing everyone non-stop.”

“To see this dog walk in and smother everyone with love, it was insane,” Anthony said as she started to cry.

“He is clearly so, so grateful to have someone show him that they care enough to give him that chance.”