Donald Trump’s personal assistant, Madeleine Westerhout, whose office sits in front of the Oval Office and who has served as the president’s gatekeeper since day one of his administration, resigned on Thursday, two people familiar with the matter said.

Ms Westerhout’s abrupt and unexpected departure came after the US president learned on Thursday that she had indiscreetly shared details about his family and the Oval Office operations she was part of.

The disclosure took place during a recent off-the-record dinner with reporters staying at hotels near Bedminster, New Jersey, in the president’s working vacation, according to one of those familiar with White House personnel, speaking on the condition of anonymity.

The breach of trust meant immediate action: Ms Westerhout, one of the people familiar with her departure said, was immediately considered a “separated employee” and would not be allowed to return to the White House on Friday.

The White House did not respond to a request for comment. Ms Westerhout did not immediately respond to an email seeking comment.

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Ms Westerhout, a former Republican National Committee aide who also worked for Mitt Romney’s 2012 presidential campaign, reportedly cried on election night because she was upset over Trump’s victory.

As such, the president at first viewed her warily, as a late convert to his cause who could not be trusted.

But some of Trump’s top officials — like John Kelly, who has since left as chief of staff — tried to turn Ms Westerhout into an ally who could help them manage Oval Office traffic.

Top Trump aide Madeleine Westerhout has abruptly departed the White House (AFP/Getty Images)

They hoped that she could block individuals from reaching the president on the phone or in person, and that she would report back on the calls and meetings that made it through.

Ms Westerhout’s power in the White House came almost entirely from proximity.

She is not a name-brand White House aide and has never appeared on television, unless it was an accidental shot of her hovering behind her boss.

But while she was not a decision-maker, she enjoyed unique access to Trump.

She also often shared snapshots on her private Instagram account of her life in the West Wing, including travel to rallies and Trump properties, and in one post she joked that she had been responsible for printing out a piece of paper that Trump held up and referred to at a public event.