John Cena and Nikki Bella Break Up

John Cena and Nikki Bella have called it quits ... calling off their engagement and breaking up.

The former couple said, "While this decision was a difficult one, we continue to have a great deal of love and respect for one another," adding, "We ask that you respect our privacy during this time in our lives."

The 40-year-old Cena proposed to 34-year-old Nikki almost a year ago to the day at Wrestlemania 33.

Earlier Sunday Cena tweeted out a quote from Walt Whitman ... "Keep your faith always toward the sunshine -- and shadows will fall behind you." He said the quote is for anyone feeling down.

John may have given a hint of trouble last month, telling Us Weekly, "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.' 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."