The scene is Mr. Musk's Los Angeles home. The time is Friday, Aug. 10. The action is what is in dispute.
Several days after Mr. Musk rattled markets on Aug. 7 with a Twitter post proposing to turn Tesla into a private company, Ms. Banks took to Instagram, where she has almost 600,000 followers, to say that she had stayed at Mr. Musk's house — an experience she likened to "a real-life episode" of the movie "Get Out." And she went on to make an explosive suggestion.
"I waited around all weekend while grimes coddled her boyfriend for being too stupid to know not to go on twitter while on acid," Ms. Banks wrote, referring to Mr. Musk's girlfriend, the musician known as Grimes.
On Thursday, in an interview with The New York Times, Mr. Musk was asked if drugs were involved in his market-moving tweet. "Absolutely not," he said.
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And then there is the question of whether they had even met.
In an interview with Business Insider on Monday, Ms. Banks said she "saw him in the kitchen tucking his tail in between his legs scrounging for investors" after his tweet about taking Tesla private, adding, "He was stressed and red in the face." On the same day, Mr. Musk told the website Gizmodo that he had never met Ms. Banks or "communicated with her in any way."
But they did lay eyes on each other, after Mr. Musk emerged from his workout that Friday morning.
Ms. Banks had arrived in the predawn hours, invited to the house by Grimes, people familiar with the sequence of events say. The two women had announced plans in June to collaborate on a project, and studio sessions were scheduled for that weekend, Grimes's representatives said.
But there was a miscommunication over the plans, Grimes's representatives said, because Grimes and Mr. Musk had instead made arrangements to go out of town.
On Friday morning, as the couple prepared to depart, Mr. Musk and Ms. Banks crossed paths.
"I saw her on Friday morning, for two seconds at about a 30-foot distance as she was leaving the house," Mr. Musk said in the Times interview. "I'd just finished working out. She was not within hearing range. I didn't even realize who it was. That's literally the only time I've ever laid eyes on her."
A Silicon Valley entrepreneur who was a creator of the internet payment system PayPal, Mr. Musk now has a home in Los Angeles. Mr. Musk, who has two ex-wives, once told Rolling Stone, "I will never be happy without having someone" — and that someone has lately been Grimes, a Canadian electronic-music singer and producer whose real name is Claire Boucher.
After it became clear that there had been a mix-up over the studio session, two people briefed on that weekend's schedule say, Ms. Banks was invited to stay on in Mr. Musk's guesthouse. She left on Sunday, these people say, and began her narrative on Instagram hours later.
Her posts soon went viral even beyond her vast social-media following. And her account of a brief interlude at the intersection of celebrity and technology was covered everywhere from Vogue to CNBC.