His two motivational books, Do Your Best Every Day To Do Your Best Every Day and Be A Work In Progress: And Other Things I'd Like To Tell My Younger Self, were released on Tuesday (April 6) and he said the Army - what BTS fans call themselves - supported him during a low point in his life.
"I was going through a pretty down period in my life. It was about four years ago and I decided to just have a vulnerable moment and put one of those thought-provoking journal entries out on Twitter," he said in an appearance on The Ellen DeGeneres Show on Monday (April 5).
"And four years ago, when I started this, a lot of them were about self-love because I was going through that down period and realising that I didn't consider myself enough."
He continued: "Amazingly enough, talk about wonderful timing and just being ready for an opportunity, the very popular group BTS had just released an album called Love Yourself."
His original tweet on Aug 27, 2018, read: "Love yourself. There will always be hatred. Striving to be better is wonderful but ALWAYS #LoveYourself. And know the difference between self-love and self-absorption. One will help you, one will not."
In his interview with DeGeneres, he said: "So I put out all these messages about self-love and I'm thinking, 'This is not going to be a good idea because this big, larger-than-life, 16-time WWE champion is now talking about vulnerability and the fact that you are enough and you shouldn't be ashamed of who you are, but it caught fire because of the BTS Army'.
"I was essentially sending a similar message of the band. And these books exist because the BTS Army was brave enough to support my vulnerable moment."
Since then, he has been posting such messages of positivity to his 12.8 million Twitter followers. Recent pithy statements from the WWE superstar include "Keeping bad people close to you is a sure fire way to keep good people away from you" and "Celebrate the wins, embrace the losses, maintain a passion for what could be possible".
His two books are a compilation of these motivational tweets, meant to encourage people during difficult times in their life. He has also written a series of best-selling children's books called Elbow Grease.
Cena, 43, who had previously professed to being a BTS fan, added: "I've really got to thank K-Pop. I've got to thank BTS for supporting me in a moment of weakness and turning it into a passion of mine."
There was even a BTS song, Fire, in his 2019 movie, Playing With Fire.
In an interview on The Late Late Show With James Corden last January (2020), he said: "Young people are listening to their music and they're sending a good message through their music.
"And I think that's really good. When you have popularity, and you choose to use your voice to do something good." – The Straits Times/Asia News Network