Donald Trump’s reporter-grabbing campaign manager, Corey Lewandowski, was fired after the billionaire’s daughter Ivanka told her dad that either he goes or she does, a campaign insider said.

“Ivanka was threatening to distance herself from the campaign if Donald didn’t get rid of him,” the source said. “Ivanka has been trying to get rid of Corey for months.”

The ax fell swiftly and left campaign chairman Paul Manafort — who had been feuding with Lewandowski — as the undisputed leader of Trump’s campaign.

The source said Ivanka Trump had been distressed by news that Lewandowski grabbed reporter Michelle Fields by the arm at a Florida event, and by a Post Page Six item reporting that he got into a shouting match on a Midtown street with campaign spokeswoman Hope Hicks.

But the final straw came when Lewandowski was “caught red-handed” trying to plant a negative story about Ivanka’s husband, Jared Kushner, the source said.

But Hicks insisted her former boss didn’t try anything of the sort.

“Absolutely not,” she said.

Lewandowski was on his normal morning call with aides Monday, unaware he was about to get the boot.

Trump’s son Donald Jr. later admitted he and his siblings played a role in his firing. “We’re obviously involved,” he told Bloomberg Politics. “We’re involved in talking with [our dad] about this, sure. But in the end, my father’s always going to make up his own mind.”

The elder Trump praised Lewandowski, but said it was time for a change. “He’s a good man. We’ve had great success,” he told Fox News’ Bill O’Reilly. “But I think it’s time now for a different kind of a campaign.

“We ran a small, beautiful, well-unified campaign. It worked very well in the primaries. But we’re going to go a little bit of a different route from this point forward. A little different style.”

Hours after his dismissal, a defiant Lewandowski sat for a lengthy interview on CNN and maintained that he had a “great relationship” with Kushner and the rest of the Trump family.

Asked whether he had tried to plant the negative story about Kushner, Lewandowski said, “I have no interest in doing that.”

One senior Trump aide told the Associated Press that Lewandowski was forced out largely because he wasn’t getting along with Republican National Committee members and GOP officials.

But Lewandowski, surprisingly, claimed Manafort was the one calling the shots.

“Paul Manafort has been in operational control of the campaign since April 7. That’s a fact,” Lewandowski said.

A Trump campaign official confirmed Lewandowski’s standing was hurt after Page Six reported about the screaming match between him and Hicks last month.

“It was the beginning of the end,” an aide said, adding that it had alarmed Trump.

“The last three weeks, [Lewandowski] was walking around the campaign with a baseball bat. Giving orders, pointing with it. Tapping people with it. Guy’s f- -king nuts,” the aide said. “Corey was down to just the interns and the airplane.”

Lewandowski’s critics made no secret of their joy at his departure.

“Ding dong the witch is dead,” Michael Caputo, a senior adviser and Manafort ally, tweeted with a photo of the vanquished Wicked Witch from “The Wizard of Oz.”

Caputo officially resigned hours later, saying he didn’t want to become “a distraction.”

“In hindsight, that was too exuberant a reaction to this personnel move,” he said in his resignation letter.

The firing came a day before Trump was to attend a New York City fundraiser organized by Woody Johnson, owner of the Jets.

Republican strategist Ryan Williams, a frequent Trump critic, said the dismissal “shows donors, activists and party officials that he is willing to make significant changes, even if it means parting ways with a trusted political aide.”

The 42-year-old Lewandowski had been a controversial figure in Trump’s campaign but benefited from his proximity to the mogul.

Often mistaken for a member of the security team, he traveled with Trump on the mogul’s private jet to nearly every campaign event, giving him more direct access than nearly any other staffer.

He was a chief proponent of the “Let Trump be Trump” strategy and dismissed the notion that the candidate had to hire more experienced hands, spend on polling and data operations, or moderate his rhetoric for the general election.

In March, Fields, then a Breitbart News reporter, accused Lewandowski of grabbing her arm after an event at Trump’s Mar-a-Lago Club in Palm Beach, Fla.

Lewandowski had mocked her claim, tweeting: “You are totally delusional. I never touched you.”

He was arrested, but the charges were dropped.

Fields had the last laugh on Monday, tweeting, “Hey @CLewandowski_ I hear @BreitbartNews is hiring.”

Meanwhile, new data released by the Federal Election Committee on Monday night showed that Trump’s campaign has only $1.3 million in the bank compared with Hillary Clinton’s $42 million war chest.

Trump’s campaign raised only $3.1 million during the month of May, to Clinton’ $28 million.

Trump, who self-funded his primary run, has been working with the Republican National Committee and holding events across the country to increase fundraising.