The pretty boy Ivy League grad who gunned down his dad more than a decade ago in Manhattan because his allowance was slashed debuted a shocking new look as he sat down for his first-ever jailhouse interview.

Sporting a scraggly beard and long locks — and apparently smelling terrible — Thomas Gilbert Jr. maintained his innocence in the 2015 murder of his hedge-fund father, Thomas Sr., at his Beekman Place pad.

The Princeton grad told Court TV’s David Scott that the spoiled “golden boy”-gone-bad narrative that gained national attention during his dramatic five-week trial “misses a lot of the other facts of the case … pertaining to my innocence.”

His childhood, he said, “was good, pretty wholesome for the most part.”

He spoke little and struggled to answer questions about his case and growing up in a life of luxury during the brief interview — but nodded affirmatively when asked if he was innocent.

Gilbert is serving 30 years to life after he was convicted of the heinous slaying.

Gilbert, known for his good looks, was 30 years old and unemployed when his parents decided to cut his allowance, which at one point was $800 a month.

After it was cut again earlier in the day to $300, Gilbert showed up unannounced at his parents’ Turtle Bay home on Jan. 4, 2015. He sent his mom out to fetch him a sandwich as he blasted his father in the head with a .40 caliber Glock.

When Gilbert’s mom, Shelley Gilbert, returned to the horror scene, she called 911 and told the dispatcher her son killed her husband.

“My son, who’s nuts. But I didn’t know this nuts,” she said, according to an audio recording.

Gilbert grew up privileged, attending the best prep schools, including Deerfield and Buckley, summering in the Hamptons and traveling the world — all on his parents’ dime.

The blond-haired surfer failed to find steady employment after graduating from Princeton with a degree in economics, instead living off his parents’ fortune. They bankrolled his country club memberships, a rental apartment in Chelsea and a Jeep.

Even after he killed his father, Shelley Gilbert paid for her son’s private attorney and argued that he belongs in a private hospital rather than a jail cell.

“He’s a sick person, who needs to be in a hospital,” she exclusively told The Post at the time. “It’s what my husband would have wanted for him if he was still here.”

The killer’s mother ended up being the prosecution’s reluctant star witness, testifying against her son after she was subpoenaed. 

A string of ex-girlfriends who testified at his trial said his behavior was strange but he was so handsome they overlooked it. 

Gilbert’s defense lawyers during his 2019 trial argued that he suffered from schizophrenia and other mental disorders and that it was psychosis and paranoia, not greed, that drove him to murder his father.

His mental illness, which the judge acknowledged as legitimate, seemed to deteriorate after he was locked up.

Several times during the trial he spoke in a rambling manner and referred to himself in the third person.

“Defendant has no criminal record, strong family ties and good behavior while incarcerated. Defendant expresses remorse,” Gilbert said ahead of his sentencing.

He was ultimately sentenced to 30 years to life in prison, despite his mother’s pleas for leniency.