Shirley Maclaine joined Downton Abbey as Cora's American mother Martha Levinson.
She appears in two episodes were she clashes with Dowager Countess of Grantham (Dame Maggie Smith).
The Hollywood star revealed that filming at Highclere Castle in Hampshire was a dream come true.
She told the Sunday Express: "Now that's a once in a lifetime experience to shoot in such a hallowed place.
"I enjoyed very, very much that castle and the grounds and the past and the haunting."
However, she admitted that she was not a fan of the Downton costumes.
The 78-year-old actress has described herself as a "jogging pants and tennis shoes" type of woman.
Discussing the costumes in the period drama, Shirley said: "I hated to put all that stuff on, I'm not one for wardrobe."
MacLaine, won the best actress Oscar in 1983 for Terms Of Endearment and was nominated for a further six Academy Awards.
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