The 34-year-old television personality vowed to "never forget" Cena after calling it quits with the 41-year-old professional wrestler in July.
Bella shared the reflective post with her 7.6 million followers on Instagram. She referenced her anniversary with Cena in the caption, writing, "8/9 | 6."
"You've changed me forever. And I'll never forget you," the message reads.
Cena posted a cryptic message on Twitter the same day.
"The promises you make mean nothing compared to those you keep," he wrote.
The promises you make mean nothing compared to those you keep.— John Cena (@JohnCena) August 9, 2018
Bella initially ended her engagement to Cena in April, but later appeared to be working on a reconciliation with the WWE star. She announced July 30 that she and Cena have officially split.
"After I called off the engagement, we tried to work on our relationship to get back to where it was, and in order to move forward with our wedding. After much time and soul-searching alone and together, we have decided to officially part ways," Bella told People.
"I had a beautiful and loving six-year relationship with a wonderful man," she said. "I have the utmost respect for John, but I know this is what's best for me."
Bella is known for her work with the WWE, and stars on the E! series Total Divas and Total Bellas.