Turbo, a baby miniature horse who was born with little use of his hind legs and recently gained some mobility from a wheelchair, died Monday, the Road To Refuge Animal Sanctuary in North Haven announced on Instagram.

Road to Refuge Animal Sanctuary founder Megan Pereira described the miniature horse, born with kneecaps in the wrong place, to Hearst Connecticut Media earlier in August as an “incredible little man.” The sanctuary rescued him from a place in Massachusetts.

“He’s got the cutest, most feisty personality ever,” Pereira previously told Hearst Connecticut Media.

Turbo’s cause of death is currently unknown, but his heart stopped and he could not be revived despite the efforts of his doctors, according to the sanctuary’s Instagram post. Before his death he had had an ‘amazing weekend’ and was grazing and comfortable, the shared sanctuary.

“Honestly, I’m numb. I never could have guessed this would happen in a million years. I asked over and over again what was wrong,” the shrine wrote on Instagram. “They don’t know. It could have been a drug reaction, a delayed anesthesia reaction, an abnormal accident. But we’re ordering an autopsy to get to the bottom of it.”

Road to Refuge Animal Sanctuary was not immediately available for comment.

Earlier in August, Turbo received a wheelchair from Walkin’ Pets, a New Hampshire-based company that creates products to help pets with disabilities. Turbo was able to run around once he got his wheelchair; it was the first time the company could help a miniature horse.

“We bought [one of our wheelchairs] as well as wheels and spacers of different sizes to adapt it to its growth and so we just assembled it on site. Before we could even fully strap him in, he was galloping, thrashing and running off,” Mikayla Feehan, Walkin’ Pets’ digital media manager, told Hearst Connecticut Media Group earlier in August.

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The sanctuary thanked those who supported Turbo in his recovery efforts with donations. Earlier in August, he underwent surgery to help repair his kneecaps.

“Thank you all for loving this adorable boy Angel as much as we do, and thank you to everyone who donated for his vet bills. Rest in peace baby boy,” the sanctuary’s Instagram post read.