'Tis no legend — the beast is real!

For four years, a hulking brown and black mastiff has been living on the lam in the woods of Brooklyn's Prospect Park, regularly glimpsed by visitors, but melting away whenever officials were called — earning him the nickname "Ghost Dog."

Until now. Sean Casey, owner of a Kensington animal shelter, finally apprehended the gentle giant this month: "I think he was ready to come in," he says, adding that Ghost Dog had been acting differently over the past two weeks, limping noticeably and lying down out in the open.

Until that point, the dog — an Italian breed of mastiff called a Cane Corso — had been a low priority.

"We realized early on that he wasn't posing a threat to anyone, so what we've done for the past two years is track him," Casey says. "He was smart. He had a schedule. He had about 12 people a day feeding him."

He also had a huge fan base. Prospect Park regulars, some of whom have referred to the dog as Brooklyn or Prospero, cherished their sightings of the mysterious pooch. And they were fiercely protective of him. Casey says that over the years, he and his tracking volunteers would be sabotaged by people who thought he was trying to catch Ghost Dog.

"They would yell to try to scare him off, wave branches," he says.

The shelter owner deduced that the dog had been abandoned by his former owner; his ears and tail are "docked," or cut, in a style common to guard dogs. But his sweet, cautious nature suggests he was never physically abused — just neglected.

When Ghost Dog began walking with a pronounced limp, Casey knew it was time for a plan. Early on the morning of May 16, he and his team formed a perimeter around an area where Ghost Dog was being fed by a local man. They moved in slowly with dog-catching poles, which they put on the ground surrounded by treats so as to make them nonthreatening.

When they did put the loop around Ghost Dog's neck, "he fought," says Casey. "He started to break the pole. I've never seen that before."

Eventually, they got him into a crate and brought him to Casey's animal shelter, where the dog tested positive for Lyme disease and was found to have bone fragments in his knee, probably requiring surgery.

Casey says he had moments of doubt: "I started to think, are we doing the right thing?"

But Ghost Dog, who is thought to be about 5 years old, has been remarkably docile since being brought in, which suggests he's ready for some TLC. As for adoption, "I'm not even thinking about that yet," says Casey.

Once Ghost Dog is healthy and trained to walk on a leash, the shelter owner will begin to sift through the many requests he's already received from people who'd like to give Ghost Dog a loving home.

It's understandable, says Casey.

"Everybody kind of felt like he was their dog."

sstewart@nypost.com