Elon Musk opened up about his on-and-off relationship with Amber Heard after the actress’ divorce from Johnny Depp: “I am often a fool, but especially for love.”

Elon Musk‘s past with Amber Heard is now an open book—literally.

The Tesla CEO and SpaceX founder reflected on his yearlong on-and-off romance with the Aquaman actress in his eponymous new biography from Walter Isaacson. As for how Elon summed up their romance, he said, “It was brutal.”

Though tech entrepreneur first met Amber after seeing her in 2013’s Machete Kills, the book said that their romance didn’t take off until four years later, after the she filed for divorce from Johnny Depp. Walter wrote that their early dates mostly revolved around work—with Amber flying to the Tesla factory in California to surprise him on his birthday and Elon visiting her on the Australian set of Aquaman—though the two did share a passion for the nerdier side of life.

“I guess I could be called a geek for someone who can also be called a hot chick,” Amber joked to the Pulitzer Prize-winning author in the biography, per People and Vanity Fair, while Walter noted in the book that the 37-year-old once spent “two months designing and commissioning a head-to-toe costume so she could role-play” for Elon, 52, after he told her that she reminded him of his favorite video game character, Mercy from Overwatch.

However, several members of Elon’s inner circle weren’t too fond of the relationship. The billionaire mogul’s brother Kimbal Musk described Amber as “toxic” and “a nightmare” in the biography, adding that Elon tends to fall for people who are “beautiful, no question, but they have a very dark side.”

His response? “Because I’m just a fool for love,” Elon told his biographer. “I am often a fool, but especially for love.”

And after he and Amber called it quits for good in 2017, Elon recalled enduring “18 months of unrelenting insanity” that was “mind-bogglingly painful.”

Kevin Mazur/MG22/Getty Images for The Met Museum/Vogue; Phillip Faraone/Getty Images for Vanity Fair

Still, the former couple is on good terms these days. “I love him very much,” Amber said in the biography, adding, “Elon loves fire, and sometimes it burns him.”

In the past, Elon has also shared kind words about his ex. “Although Amber and I did break up, we are still friends, remain close and love one another,” he shared on Instagram August 2017. “Long distance relationships when both partners have intense work obligations are always difficult, but who knows what the future holds.”

Last year, he also shared his well wishes for Amber shortly before she was found liable for defaming her ex-husband Johnny in a jury trial in Virginia. “I hope they both move on,” he wrote on X (formerly Twitter), the social media site he purchased in 2022. “At their best, they are each incredible.”

E! News has reached out to Amber and Elon’s reps for comment but hasn’t heard back.