The former pro-wrestler, whose name is John Anthony Paul, said it "sucks" that the Total Bellas star decided to once again end her relationship with Cena.
"I know John Cena was really in love with her. I've never seen him like that," the former Cryme Tyme tag team member told TMZ during a quick interview with the outlet.
JTG said he has known Cena for quite some time — including during his marriage to ex-wife Elizabeth Huberdeau — but added, "I've never seen him head over heels for a female like he was with Nikki."
The interview comes as reports surfaced earlier this week that Bella and Cena were officially done, as they had told friend there was no more hope for a reconciliation.
Bella is also reportedly moving out of their San Diego home together and focusing on finding her own spot and building her own career.
"It's tough, because he's fighting really hard for me," she told her family on Sunday's Total Bellas season finale. "There's something that is making me not feel like I can walk down that aisle. And that doesn't mean ever with him, I just can't do it right now."
Though she admitted how she still loved Cena, she feels like she's "ruined everyone's fairytale," and didn't want to end up down the road in a marriage that was unhappy due to her desire to please other people.
"I didn't give myself long enough when we called it off the first time...I just realized there's deeper problems," she said of the first time she called off their engagement. "To have a happy, healthy lifetime with him, I have to take a while for myself."
Bella recently offered an update on the pair's current relationship status in a YouTube video, saying that she and Cena are just friends for now.
"We are both working on each other and trying to work on us. We talk every day. He is not only my best friend, he is truly one of the most amazing people I've ever met, and he has patience with me, and he has really taught me a lot over the past few months. I think one of those things is an inner strength that I thought I had but didn't realize how strong I had it," she said, adding that Cena's time in China was "giving us this time in life to see what we want in the future."