Elon Musk’s biographer says the most painful thing in the billionaire’s life was his relationship with Amber Heard.

Walter Isaacson said on Kara Swisher’s podcast that “nothing hurt me more than that relationship.” Isaacson said the relationship was full of “storms and turmoil” that were “part of the attraction.”

Elon Musk’s biographer says the billionaire’s relationship with actress Amber Heard hurt him the most, even more than Musk’s strained relationship with his father.

“The storm and the turmoil that both sides are talking to me about is not a point of contention, it was part of the attraction,” Walter Isaacson said on the latest episode of the “On With Kara Swisher” podcast. “Part of the theme of this life is that this person is attracted to drama and storm. When things are calm, he comes out — he buys Twitter or whatever. So that’s true of his relationship with Amber. Nothing hurt him more than that relationship.”

Musk and Heard’s lawyer did not immediately respond to requests for comment.

Musk and Heard dated on and off after getting close at the 2016 Met Gala. They went public with their relationship in April 2017 before announcing their split a few months later. They continued to see each other after their split before breaking up again in 2018.

Isaacson spent two years following Musk for the biography, which hit bookstores last week.

The book describes the “psychological upheavals” that have marked many of Musk’s romantic relationships. It recounts Musk’s first meeting with Heard: She asked him if she could visit SpaceX a year after the two men had worked on the action movie “Machete Kills,” with Heard as the star and Musk as a consultant.

Isaacson also documented the explosive arguments in their relationship, writing: “She and Musk would stay up all night arguing, and then he wouldn’t be able to get up until the afternoon.”

In the biography, Heard said she liked Musk “a lot,” but that “Elon likes fire and sometimes he burns it.”

When Isaacson asked Musk to explain his tumultuous love history, the billionaire replied: “I’m often a jerk, but especially in love.”

Canadian musician Grimes, Elon Musk’s ex with whom he shares three children, told Isaacson for the biography that Musk “associates love with being mean or abusive,” in part because of his relationship with his father, Errol Musk.

Elon Musk has said that his father bullied and humiliated him throughout his life. In 2017, he told Rolling Stone that his father was a “terrible human being” who did “almost every bad thing imaginable.”

Errol Musk has denied reprimanding his son.

Elon Musk’s first wife, Justine Wilson, whom he was married to from 2000 to 2008, has opened up about their relationship.

“There’s a combative side to him,” she told Isaacson. “I don’t think you can be in a relationship with Elon without fighting.”

“When you come from a dysfunctional background or have a brain wired like his,” Wilson told Isaacson, “intensity replaces intimacy.”