From Downton Abbey to Brooklyn Federal Court.

A British aristocrat who counted late Prime Minister Margaret Thatcher as a pal and hosted George Bush Sr. at his 17th century manor has thrown his unlikely support behind an illiterate Irish gypsy who admitted selling endangered black rhino horns in Queens.

Lord Vincent Constantine — who resides in a sprawling Cambridgeshire compound named Crosshall Manor — submitted a letter of snobbish endorsement for Michael Slattery Jr., a purported member of a shadow band of Irish gypsy crooks.

Dripping with pretension, Constantine suggests to the court that the vulgar situation should not be taken too seriously, as the crime was borne simply out of “stupidity and ignorance,” according to his brief missive.

Constantine explains that he occasionally did business with Slattery Jr.’s father in the antique business and found the suspect to be a delightful young man.

“I have known Michael Slattery Jr. for over 10 years and I can honestly say throughout that time I found him to be a trustworthy and courteous young man,” the lord wrote. “I was extremely suprised to learn that he had been arrested and can only think his actions were taken out of stupidity and ignorance as they are totally out of character.”

Lord Constantine once noted in an interview about his garden that he “imported ericaceous soil in one part to allow [him] to grow acers and rhododendrons successfully,” which could be a sound bite from the upper-crust hit PBS soap “Downton Abbey.”

Slattery Jr., 23, traveled from London to Texas in 2010 to buy two rhino horns and hired a day laborer to sign off on illicit paperwork.

He later sold the items to a Chinese buyer in Queens before getting arrested at Newark Airport.

Slattery Jr. is a purported member of the Rathkeale Rovers, a shady band of Irish nomadic crooks who conduct illegal business around the world from the tiny town of Rathkeale in Ireland.

The redhead finds himself a world removed from Crosshall Manor. In his most recent court appearance, Slattery Jr. complained to Judge John Gleeson about the trying environment in his Brooklyn lockup that included having a murderer for a cellmate.

Slattery Jr. faces five years in prison; his lawyers are asking Gleeson to sentence him to time served, or about two to three months.

In addition to the letter from his lordship, Slattery Jr. also submitted messages of support from other luminaries from his tiny home town in County Limerick.

In a one-sentence contribution, Rathkeale top cop Michael Shiels wrote, “I have known Michael Slattery Jr. all his life and to the best of my knowledge he has never been in trouble with the law.”

Retired Rathkeale priest Maurice Costello backs Slattery Jr. as well, calling him a “very nice and hard working young man.”