Shirley MacLaine (Evan Agostini/Getty Images)

Thankfully, the show features an American-born Lady Grantham character, played by Elizabeth McGovern, so MacLaine can play her mother convincingly, even with her flat mid-Atlantic accent.

That, in marked contrast to that time MacLaine played the legendary French designer Coco Chanel with a flat mid-Atlantic accent, in a 2008 Lifetime bio-flick about Chanel.

When asked by TV critics why she wasn’t asked to do an accent — given that the young Coco in the flick’s flashback scenes had a heavy French accent — MacLaine responded peckishly that it’s because “I wouldn’t have done it.”

“I’m not Meryl Streep,” MacLaine snapped.

“You don’t ask Sean Connery to play with a French accent; you don’t ask Shirley MacLaine to play with a French accent,” added Coco Chanel director Christian Duguay, jumping in, during that testy Summer TV Press Tour 2008 encounter.

Critics were too polite to note that no one had asked Sean Connery to play Coco Chanel.

Anyway, “Masterpiece” executive producer Rebecca Eaton seems to get it, noting in Monday’s announcement: “Shirley MacLaine is a great actress and she’s as American as the day is long.”

Eaton also promised that there would be much sparring in the show between MacLaine’s character and Maggie Smith’s Lady Violet. My money’s on Smith, no matter how the scenes are written.

Anyway, Gareth Neame, managing director of the series’ producing partner Carnival Films, noted that he’s particularly pleased with the casting of MacLaine because his dead grandfather directed her in “Gambit” in 1966.