Britney Spears' Spiral Started 'With How Justin Timberlake Treated Her,' Claims Source: 'He Destroyed' Her

Britney Spears has experienced massive amounts of heartbreak — but none was more significant than her shattered romance with Justin Timberlake.

In her bombshell memoir, The Woman in Me, the pop icon, 41, detailed the ups and downs of her tumultuous teen love affair with the "Cry Me a River" singer, which insiders say triggered her continuous downward spiral.

"Looking back, it all started with how Justin treated her," a source spilled to a magazine. "He destroyed Britney."

In the massively successful tell-all, Spears penned of Timberlake, 42, "There were a couple of times during our relationship when I knew Justin had cheated on me. Especially because I was so infatuated and so in love, I let it go, even though the tabloids seemed determined to rub my face in it."

"When NSYNC went to London in 2000, photographers caught him with one of the girls from All Saints in a car. But I never said anything. At the time we'd only been together for a year," the "Toxic" vocalist detailed.

In another extremely difficult moment, Spears became pregnant with the Friends With Benefits star's baby. However, Timberlake allegedly convinced his then-girlfriend to undergo an abortion. "It was a surprise, but for me, it wasn't a tragedy. I loved Justin so much. I always expected us to have a family together one day. This would just be much earlier than I'd anticipated," she wrote.

"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," the blonde beauty noted. "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."

"To this day, it's one of the most agonizing things I have ever experienced in my life," Spears said of the excruciating decision.

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Their relationship — which lasted from 1999 until 2002 — ultimately ended via a text from Timberlake that Spears received while working on a music video set.

"After seeing the message as I sat in my trailer in between takes, I had to go back out and dance," she explained. "For as much as Justin hurt me, there was a huge foundation of love and when he left me, I was devastated. When I say devastated, I mean I could barely speak for months. Whenever anyone asked me about him, all I could I do is cry. I don't know if I was clinically in shock, but it felt that way."