Married Republican South Dakota Gov. Kristi Noem has engaged in a years-long affair with longtime Donald Trump adviser Corey Lewandowski, multiple sources told The Post Friday.

The liaison emerged one week after Noem, a 51-year-old mom-of-three, formally endorsed Trump, 77, for the 2024 Republican presidential nomination, raising the pitch of speculation that the 45th president would pick her as his running mate.

“He’s 100% banging her,” said one person familiar with the relationship between Noem and Lewandowski, first reported by DailyMail.com.

The source added that they personally witnessed Noem “sitting on his [Lewandowski’s] lap” and “playing grab-ass” during an event at Trump’s Mar-a-Lago resort in March 2020.

“The usual stuff that drunk people who are having affairs do,” the source described the interaction.

A second source told The Post the dalliance has been widely known of in Republican political circles for “years,” adding that Noem’s husband is said to have moved out of the governor’s mansion in Pierre roughly two years ago.

A third source told The Post that he and fellow GOP operatives were “well aware” of the fling and suggested the story finally appeared in print thanks to “one of her competitors for VP.”

Both Trump and political pundits have publicly mused for months about potential running mates, with some of the names mentioned including Noem, former Arizona gubernatorial candidate Kari Lake, former Secretary of State Mike Pompeo, Sen. Marsha Blackburn (R-Tenn.), former ambassador to Germany Ric Grenell, House Republican Conference Chair Elise Stefanik (R-NY), current GOP presidential candidate Vivek Ramaswamy, and hard-right Rep. Marjorie Taylor Greene (R-Ga.).

Noem herself was once considered a potential 2024 contender but opted not to enter the race, telling Fox News last month that no Republican could win the nomination as long as Trump was running.

“Why run if you can’t win?” she asked.

On Sept. 8, Noem announced at a rally in Rapid City that she was backing Trump, calling him “the fighter that our country needs.”

“You made America great again once, let’s do it again,” Noem said while introducing the former president. “I will do everything I can to help him win and save this country.”

Lewandowski, 49, was Trump’s first 2016 campaign manager and widely credited with engineering his victory in the 2016 New Hampshire primary, which bolstered the real estate mogul after a loss to Sen. Ted Cruz (R-Texas) in the Iowa caucuses.

However, Lewandowski’s start began to fade after he was accused of manhandling Breitbart reporter Michelle Fields following a Trump press conference in March 2016.

He was charged with one count of simple battery, which was later dropped.

Lewandowski was dismissed from the Trump campaign three months later, following reported clashes with then-campaign chairman Paul Manafort.

Representatives for Noem did not immediately respond to requests for comment.

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