In his new book, "Hindsight: And All The Things I Can't See in Front of Me," Justin doesn't name Britney by name, but he reveals that the song was written after a 2002 breakup, which is when he and the pop princess split.
There have been reports over the years that imply that Britney was unfaithful to Justin, which he also hints at in the song.
"I've been scorned. I've been pissed off. The feelings I had were so strong I had to write it," he said in the book. "I translated my feelings into a form where people could listen and hopefully relate to it. People heard me and they understood it because we've all been there."
That all seems to be water under the bridge for Justin, as he is now married to Jessica Biel.
Jessica, whom he married in 2012 after several years of dating, "changed me. She changed my life," he wrote.
The two share 3-year-old son, Silas.
"She's been a huge influence on my life, and I have such admiration for her, especially seeing her as a mother now," he said.
He added that Jessica is a different person than the woman he met over 10 years ago.
"I've watched my wife change. I've watched her body change," he wrote. "It's a temple. It should be worshiped. It should be marveled at. I'm fascinated by her. She's everything, man. I wake up and roll over and look at her, and I'm inspired."