Elon Musk was rushed to the emergency room and needed stitches and a tetanus shot after his brother Kimbal bit off a piece of flesh from his hand during a fight, according to an upcoming biography of the Tesla mogul.

According to author Walter Isaacson, Kimbal Musk bit Elon Musk’s hand because he thought his brother was about to punch him in the face while they were both running the startup Zip2 more than two decade ago.

An excerpt of Isaacson’s biography was cited by the news site Insider.

While co-running Zip2, which provided city guides to newspapers, the two brothers would often have “rolling-on-the-office-floor fights,” according to Isaacson’s biography of Elon Musk.

The fights took place in full view of Zip2 staffers since the company did not have private offices, Isaacson reported.

“When we had intense stress, we just didn’t notice anyone else,” Kimbal Musk told Isaacson.

The Musk brothers ran Zip2 until they sold the company to Compaq Computer in 1999 for $305 million. Elon Musk pocketed $22 million from the sale while Kimbal Musk earned $15 million.

Isaacson’s book details Kimbal Musk’s misgivings about his brother’s social media habits, particularly the toll it was taking on Tesla, the electric car maker.

Kimbal Musk, who is a member of the board of directors of the company run by his brother, was said to be embarrassed by his sibling’s antics on X.

“The giant elephant in the room was that he was acting like a f–king idiot,” Kimbal Musk is quoted as saying by Isaacson.

The posts by Elon Musk were “too nerve-racking” for Kimbal Musk — so much so that the latter stopped following the former’s online activities, according to Isaacson.

Musk’s posting online also earned him admonishment from peers in business.

Warner Bros. Discovery CEO David Zaslav told Elon Musk that he was having trouble attracting top advertisers because of the “self-destructive” manner in which he ran the social-media giant, according to a new book.

Media mogul Zaslav spoke to Musk for more than an hour during a tumultuous period for the company formerly known as Twitter, which was acquired by the latter for $44 billion last year.

According to Walter Isaacson’s biography of Musk, which is set for release on Tuesday, Zaslav urged Musk to focus on improving the company’s product.

It is unclear when the conversation took place.

The anecdote from Isaacson’s book was cited over the weekend by The Wall Street Journal.

Isaacson’s book also details Elon Musk’s difficult in managing relationships with people, particularly employees.

According to Isaacson, Musk once threatened to fire a staffer at SpaceX, his rocket-building company, while completely unaware that the employee and his wife had just lost a newborn baby.

The SpaceX worker, a financial analyst, was grilled by Musk over an issue related to parts in the engine of the company’s Starship rocket.

According to Isaacson, Musk made it clear that he would demand the employee’s resignation if his job performance didn’t improve.

Gwynne Shotwell, Space’s president, reportedly noticed that the staffer’s job performance had tailed off in the weeks prior due to the fact that he and his wife lost their baby, according to the book.

Musk was not aware of the couple’s ordeal, Isaacson reported.

The Post has sought comment from SpaceX, X, and Warner Bros. Discovery.

Musk acquired Twitter and followed through on his pledge to un-ban controversial figures whose accounts were suspended or deactivated by the previous management due to violations of its content moderation policies.

The move by the self-described “free speech absolutist” spooked advertisers who fled the platform, prompting Musk to lash out at “activist groups” who were “pressuring” brands “even though nothing has changed with content moderation and we did everything we could to appease the activists.”

“Extremely messed up! They’re trying to destroy free speech in America,” Musk added in a post on his social media platform just weeks after the acquisition.

Musk last week threatened to sue the Anti-Defamation League after he alleged that the civil rights group falsely accused X of fomenting anti-Semitism — resulting in a flight of advertisers from the site.

X over the weekend vowed to step up enforcement of content moderation rules as they relate to anti-Semitic content.

Elon Musk has run into trouble for his social media habits.

In 2018, the Securities and Exchange Commission charged him with securities fraud for misleading investors after he posted an item suggesting he would take Tesla private at $420 per share.

The number “420” is a slang term in cannabis culture which connotes consumption of marijuana and hashish.

Musk paid a settlement to the SEC. As part of the deal, he pledged to have his social media posts vetted.