The 1920s-set series was Sunday night's most-watched scripted show, Variety reported.
About 7.9 million U.S. viewers tuned in for the Season 3 premiere of "Downton" last January, the entertainment industry trade newspaper said.
Starring Hugh Bonneville, Elizabeth McGovern, Maggie Smith, Michelle Dockery, Jim Carter, Joanne Froggatt and Brendan Coyle, the show starts airing in the United States after each season wraps in the United Kingdom. The U.S. run of Season 4 is to end Feb. 23.
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