On June 16, 2015, 23-year-old Gypsy Rose Blanchard walked into a Wisconsin courtroom in handcuffs, implicated, along with her boyfriend, in the murder of her mother, 48-year-old Dee Dee Blanchard, who had been found stabbed in their Missouri home.

But more shocking than the murder itself was that Gypsy — known to friends, neighbors, even her father to be wheelchair-bound since childhood — could walk.

“I was happy that she was walking and then . . . Wow, total shock,” Rod Blanchard, Gypsy’s father and Dee Dee’s ex-husband, tells The Post. “What has been going on all of these years?”

The bizarre case of matricide is the subject of the documentary “Mommy Dead and Dearest,” airing May 15 on HBO. Directed by Erin Lee Carr, the film explores Dee Dee and Gypsy’s twisted story and resulting murder investigation to reveal decades of abuse related to Munchausen by proxy syndrome, a psychological condition in which a person acts as if an individual in their care has a physical or mental illness when that person is not really sick.

The crime was a tragic end for a pair that seemed to have an unbreakable bond. In the film, neighbors recall being impressed by the selfless Dee Dee, who devoted all of her time to caring for her ailing daughter, who suffered from a laundry list of maladies, including muscular dystrophy and leukemia.

“They were inseparable. They did everything together,” Kristy Blanchard, Rod’s wife and Gypsy’s stepmother, tells The Post. “Dee Dee and I had talked about it on several occasions, that if something ever happened to her, she would hope they would both go at the same time because one couldn’t live without the other.”

That made the June 14, 2015, Facebook post on the mother-daughter’s joint account — “that Bitch is Dead” — all the more shocking. Investigators traced the post to Big Bend, Wis., where they arrested Gypsy Rose and her boyfriend, Nicholas Godejohn, 26, whom she met on a Christian dating site, and who is charged with carrying out the murder at Gypsy’s request.

Carr first learned of the case from her co-producer, Alison Byrne, in August 2015, and wrote to Gypsy in prison. She visited her twice for off-the-record meetings before nabbing an exclusive courtroom interview with her — a highlight of the documentary — in July 2016, on the day Gypsy accepted her 10-year plea deal for second-degree murder.

“Her whole life, she’s had to participate in impression management — in front of her mom, in front of other people who think she’s handicapped,” Carr says.

“She acted completely different [in those initial visits],” Carr adds. “It was like talking to someone who was 15; it didn’t feel like a mid-20s woman. But as we got more comfortable, she was able to shed that little-girl behavior. She was really articulate.”

What Carr pieced together — through interviews with Gypsy, her family members, friends and neighbors; home videos and family photos; and medical records — paints a picture of Dee Dee as a master manipulator who wanted to keep her daughter young forever.

Rod recalls Dee Dee — to whom he was briefly married, though they separated before Gypsy was born — told him their baby was suffering from sleep apnea at 3 months old. Her reported medical issues snowballed from there: muscular dystrophy requiring the use of a wheelchair; seizure medication that made her teeth fall out, requiring doctors to implant a feeding tube; leukemia. Gypsy was home-schooled after second grade on claims of her limited mental capacity.

All would turn out to be unfounded.

Carr obtained medical records that show dozens of hospital visits and multiple surgeries to treat Gypsy’s symptoms, often brought on by all the medications Dee Dee gave her. When one doctor raised the possibility of Munchausen’s, Dee Dee switched doctors, and his report allegedly became lost in hospital bureaucracy.

Her family members, friends and neighbors; home videos and family photos; and medical records paint a picture of Dee Dee as a master manipulator who wanted to keep her daughter young forever.

“I really, genuinely believed that she had some issues,” Rod says. “Dee Dee was really good at convincing me that there was a problem. I never, ever can fathom that she was really in the hospitals, and the doctors wouldn’t have caught on to something at some point over the years.”

As Dee Dee and Gypsy moved farther away from Rod and Kristy’s home in Cut-Off, La., they stopped seeing them in person; their last visit was when Gypsy was 12 years old. When the pair settled in the Missouri Ozarks in 2008, Rod continued to call his daughter several times a year and Dee Dee would keep him informed of Gypsy’s supposedly worsening condition.

Rod believes people on Dee Dee’s side of the family may have had their doubts. At the time of the murder, Dee Dee’s nephew, Bobby Pitre of Larose, La., who is also interviewed in the film, told an NBC station that when relatives confronted Dee Dee about her treatment of Gypsy, she cut off communication with them.

“It was basically all a fraud,” he said. “I was so disgusted with the woman. I could not believe what she was doing.”

Meanwhile, Dee Dee was accepting financial donations for Gypsy’s medical care. They went on trips to Disney World sponsored by charitable organizations and lived in a house built by Habitat for Humanity. When the murder revealed the lengths of Dee Dee’s deception, former friends and some in the media accused the rest of the Blanchard family of being in on the scam.

“We weren’t aware of any of it. None whatsoever,” Kristy says. “When they were going on vacation, Rod would send her extra money . . . If [Dee Dee] could fool her neighbors and everybody else, it was easy to fool us, because we were so far away.”

One of the issues the film tackles is Gypsy’s own culpability: If she knew she could walk, why didn’t she say anything all these years? Why didn’t she escape? How complicit was she in orchestrating the charade?

“She could have run away, she tried to, but none of us know what it was like to exist in a house where you were held hostage in a wheelchair for that many years,” Carr says. “She liked going to Disney World, she liked the presents, the attention. She had to stay in a wheelchair forever — she had to take joy in these small pleasures.”

“I do not think Gypsy was lying about being physically assaulted [by her mom],” Carr adds.

When Gypsy met Godejohn, she found a way out. In their online relationship, they bonded over their love of Disney movies, and participated in role play. When she confided in him about Dee Dee’s controlling nature, a plan was formulated to kill her.

As seen in the film through text messages between the two and never-before-seen interrogation-room footage, Godejohn took a bus to Springfield, Mo., slipped into the house while Dee Dee slept and allegedly stabbed her while Gypsy hid in the bathroom. According to their statements to investigators, they then cleaned up the crime scene, fled with several thousand dollars from Dee Dee’s safe and made their way to his parents’ house in Wisconsin, where they were busted days later.

Carr’s requests to speak to Godejohn or his lawyer for the documentary went unanswered. From watching his entire interrogation footage, Carr says, “I think he is a severely mentally ill person who got a bad end of this.” He and Gypsy do not speak anymore. Godejohn is currently awaiting trial and faces life in prison.

Gypsy, meanwhile, is serving her 10-year sentence in Chillacothe Correctional Institution in Ohio, where she’s working toward her GED. She’ll be eligible for parole in 2024, at the age of 32. Rod and Kristy talk to her often, and visit her when they can.

“It’s really hard on her some days. She says, ‘I just want to go home, I just want to be home with you all,’ ” Kristy says.

“We went to see her in March and she looks great. From that first picture that they posted of her when she got arrested [to now], total transformation. She’s more confident, she walks with her head held high. She talks more, she’s opening up to us more.”

Kristy says she has forgiven Dee Dee, though Rod still carries anger toward the mother of his child and blames himself — “there’s a million things I could have done differently” — for not seeing through the deception that led to such a violent crime.

“How do you kill your own mother? You had to have been put through some serious trauma, abuse, to be able to consciously make that decision,” he says. “I couldn’t imagine what she was going through.

“I think if Dee Dee was right here, right now, I might do the same thing that Gypsy did,” he adds. “It’s absolutely horrifying that you can do that to your child.”