Prosecutors say that the failed stockbroker charged with murdering his estranged banker wife did so with a chokehold — and disclosed for the first time in court Monday that the defendant had demonstrated the martial arts move in jail.

Just last week, defendant Rod Covlin’s attorney Robert Gottlieb argued that there was no proof his client, who has a black belt in Taekwondo, could perform such a maneuver, and that the prosecution’s expert martial arts witness should be barred from testifying at the trial.

But Assistant DA Mathew Bogdanos said that jailhouse surveillance video he had just obtained from the Brooklyn Detention Complex’s law library contradicted that claim.

“That video shows the defendant demonstrating a chokehold to another inmate,” Bogdanos told Justice Ruth Pickholz shortly before the start of jury selection in Manhattan Supreme Court.

The prosecutor wants to introduce the footage during testimony from the martial arts expert, who will say that Covlin is performing the move correctly, and the medical examiner, who will say the chokehold is consistent with Shele Danishefsky’s broken neck.

Gottlieb objected to the last minute request to introduce the video filmed in November of last year.

There’s no evidence he was taught that chokehold or knew about it at the time it was relevant to this case,” Gottlieb blustered. “ There is no basis. It’s absurd. It’s ridiculous and should have no part in this trial.”

The judge said she will watch the footage then make her decision.

Danishefsky was discovered face-down in the bathtub of her Upper West Side apartment by her 9-year-old daughter, Anna, on New Year’s Eve. Her brother, Myles, had been asleep.

Covlin and his wife, who were living in separate apartments on the same floor, were in the midst of a contentious divorce and custody battle over their two children.

Authorities initially considered the death an accidental drowning, but an autopsy conducted three months later revealed that she had a broken neck bone.

It wasn’t until 2015 that Covlin was finally charged with her murder after blabbing to his girlfriend about what he’d done.

The trial is slated to begin next week.