“If it had been left up to me alone, I never would have done it,” she writes of the procedure, according to the excerpt from The Woman in Me published in People magazine.

“And yet Justin was so sure that he didn’t want to be a father.”

The pregnancy “was a surprise, but for me, it wasn’t a tragedy,” she wrote in the excerpt, saying that she had wanted to start a family with Timberlake – it was just earlier than expected.

“But Justin definitely wasn’t happy about the pregnancy. He said we weren’t ready to have a baby in our lives, that we were way too young,” she wrote.

The couple broke up in 2002, although it’s unclear when the pregnancy happened.

Representatives for Spears declined to offer further comment. Representatives for Timberlake did not respond to requests for comment from The Associated Press.

Spears, a prolific user of social media, has not posted to Instagram or X, the platform formerly known as Twitter, since the People stories were published.

In the excerpt published in People, she characterised the abortion as “one of the most agonising things I have ever experienced in my life.”

Spears has since gone on to have two children – Sean Preston, 18, and Jayden James, 17 – with her second husband, Kevin Federline.

Spears’ long-awaited memoir will be published on October 24, just months after her divorce from Sam Asghari.

The memoir is set to be released two years after the end of her conservatorship, which Spears writes in the book “stripped her of her womanhood”.

The US singer has previously called the arrangement abusive. It was set up by her father in 2008 after she experienced a public breakdown, during which she shaved her head.

Spears testified to a court in 2021 that she had been drugged, forced to perform against her will and prevented from having more children under the conservatorship.