.
"This would just be much earlier than I’d anticipated. 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. I’m sure people will hate me for this, but I agreed not to have the baby. I don’t know if that was the right decision.
"If it had been left up to me alone, I never would have done it. And yet Justin was so sure that he didn’t want to be a father."
The star said the abortion was "one of the most agonizing things I have ever experienced in my life" in the memoir - which is set for release on October 24.
BRITNEY'S BROOD
Britney had her first child, son Sean Preston, with her now ex-husband Kevin Federline in 2005 and her second son, Jayden James, in 2006.
Justin went on to marry The Illusionist actress Jessica Biel, 41, in 2012 and the couple share sons Silas, eight, and Phineas, three.
The U.S. Sun exclusively revealed this week that Justin and Jessica will have been left reeling from Britney's bombshell claims.
A source said: "Justin owns who he was when he and Britney were together, even though his personality, career, lifestyle, and personal priorities are radically different now, 20 years later.
“This book is a nightmare for him because of how it throws the whole family into chaos. The timing stings just as much as the revelation itself."
The insider continued: "Justin had a big fall planned with new music on deck, more work with his old friends in 'NSYNC, and of course, the next installment of the Trolls franchise, which has been a huge moneymaker for Justin over the last several years.”