In 2016 the WWE icon said he did it for a "sense of security" and again opened up on it earlier this year.
"I was very abrasive and stern and she had to sign this huge, crazy agreement just to come in the front door," Cena said on the Today show.
Cena also said Bella signed the agreement "totally without question and it made me feel super bad, which it should have, but it also made me realise, like, this is one young woman I should not let get out of my life because she says, 'I'm with you because I love you, here's proof I would still like to be here'".
Bella spoke about her confusion at having to sign the document in an episode of her reality TV show Total Bellas.
"Is that all I'm ever going to be in (his) heart, is a guest? Am I ever going to have that permanent spot in the rest of (his) life?" she said.
"I just don't understand it. I just don't know what to feel. I'm so confused. It kind of makes me second-guess where John and I stand in our relationship. I love John but maybe he knows that he doesn't want to be with me forever?"
Bella announced the longtime couple were splitting up in a post on Instagram Monday.
"After much contemplation and 6 years of being together Nikki Bella and John Cena announced today their decision to separate as a couple. While this decision was a difficult one, we continue to have a great deal of love and respect for one another. We ask that you respect our privacy during this time in our lives," the post read.
Only seven days ago, Nikki posted on her Instagram account a remake of the moment Cena proposed to her with the caption stating she was "the luckiest girl in the world".
They often took their relationship public, canoodling on red carpets and talking about each other in interviews. The wedding was reportedly scheduled for May 5.
Cena then took to his own personal Instagram page hours after the statement of the shock split was released and expressed his feelings surrounding the decision to split after the year-long engagement.
Cena has made a successful transition from wrestling to acting but also made a surprise appearance at WrestleMania where he took on wrestling legend The Undertaker.
He has appeared in movies like Daddy's Home and Daddy's Home 2 along with the new R-rated comedy Blockers. He received rave reviews for his role in the 2015 comedy Trainwreck.
Bella stars in a reality TV show on E! called Total Bellas with her twin sister, Brie.
The multiple WWE champion spoke about the difficulties of the relationship and the hard work it takes.
"It takes being able to mesh two lives. I would never ever want Nicole to be in a position where she says, 'I'm holding you back from doing this because I feel it's wrong for us,'" Cena said to Us Weekly.
"And I would never say that to her. That's why she's super busy and sometimes we don't see each other for months at a time, but when we do see each other, it's our time together. I think, for now at least, that is certainly what's making this work."
— with AP
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