On Monday (April 16), John Cena and Nikki Bella broke the news that they were splitting up just weeks before their May 5th wedding. But after six years together, what could have happened between the famous WWE couple to make them call it quits?

According to ET, there was one main issue that caused the separation. A source told the outlet that issue was starting a family.

"Nikki and John truly love each other, but they will never have the same view on a perfect future," the source tells ET. "Nikki has always dreamt of having a family of her own and John does not want children and that was the main cause of their break up. They are both dedicated to their careers, but Nikki wants more than just that."

"Nikki thought at one point she could get past wanting children and that her love for John was enough, but as time went on, she has realized her dreams of a family would never happen with John," the source continues. "She couldn't get past the idea of not having her own baby."

Cena has publicly spoken out about not wanting children, including on Nikki and her sister Brie's reality series, Total Bellas.

"Some people just don't want children. Everyone wants to blame John, but he feels he was honest and upfront with Nikki about never wanting to have children," the source says. "John's mistake was to then propose, because he knew that is what Nikki wanted most. He meant well, but in the end, it only hurt Nikki more and prolonged the inevitable."

"He began to make promises to Nikki that he just couldn't fulfill," the source adds. "Nikki wanted nothing more to believe that he had changed and he was trying but it wasn't enough. John felt as if he was really giving up part of himself by getting married. Bella felt she was giving up her opportunity to have children if she spent her life with John and eventually neither of them could get past it."