A doctor in England wore a ridiculous disguise — replete with a cheap wig and phony facial hair — so he could poison his mother’s partner, clearing the way for his own inheritance, the physician admitted Monday in court.

Thomas Kwan, 53, pleaded guilty to attempted murder for shooting a pesticide into the arm of his mom’s 71-year-old beau, Patrick O’Hara, which gave him a “rare and life-threatening flesh-eating disease” back in January, according to the BBC.

The devious doc had previously denied the charges in Newcastle Crown Court — as prosecutors claimed he went to extraordinary lengths to fashion “one of the most elaborate criminal plots in recent memory,” according to the Guardian.

Kwan, a native of Hong Kong who lives about an hour south of his mom’s northern England home, admitted giving O’Hara the toxic shot, but at first claimed he’d only wanted to cause his victim some pain and discomfort.

At the trial’s opening, prosecutor Peter Makepeace called Kwan’s plot an audacious, stranger-than-fiction story meant to avenge his mom’s decision to leave her house to her longtime lover when she died.

The well-respected general practitioner was obsessed with money, Makepeace said, and hatched the twisted plan to eliminate O’Hara by donning a dead-rat wig and wispy facial hair, then claiming he was from the country’s National Health Service, according to the outlet.

He sent a letter to his victim saying he was eligible for a medical checkup by a community nurse who would come to his Newcastle home.

“As, I suspect, would any of us, Mr. O’Hara fell for it hook, line and sinker; he had not the slightest suspicion that this was anything other than a genuine NHS community care initiative which he warmly welcomed and was grateful for,” Makepeace said in court.

When Kwan arrived at O’Hara’s home on Jan. 22, he wore tinted glasses, a medical mask, a hat and gloves as he carried out a full exam on his mom’s unsuspecting lover, the Guardian reported.

He also told O’Hara that he needed a COVID-19 booster shot, which he administered.

But it was no vaccine the clinician shot into the man’s arm — scientists later figured out the vial was likely full of the pesticide iodomethane.

O’Hara became was suspicious when he realized the “nurse” was the same height as his beau’s son, and sought medical help after the shot — which caused a “terrible pain” at the injection site — turned his arm white and blistery.

His instincts proved right — doctors at Newcastle’s Royal Victoria Infirmary had to treat him for necrotizing fasciitis and remove parts of his arm, the prosecutor told the court.

He spent several weeks in the intensive care unit, the Guardian added.

When cops searched Kwan’s home, they found chemicals, toxins and books on how to make and use poisons, according to the outlet.

Kwan — who’d done other shady things to his mom and her lover, such as install spyware on her computer — had also come up with at least two backup plans in case his primary plot failed, prosecutors said.

He eventually pleaded guilty, and his attorney said he’d accepted that prison was inevitable.  

Kwan will be sentenced Oct. 17 — and the judge said he can expect “substantial” prison time.

DCI Jason Henry of Northumbria Police called Kwan’s actions “utterly despicable,” and said the horrendous ordeal had changed O’Hara’s life forever.

“He has shown incredible strength throughout the investigation,” the cop said of O’Hara. “We will continue to support him in any way we can.”