Ngannou made an appearance on Joe Rogan's "JRE MMA Show" Tuesday and he talked about a wide range of subjects, including the moments he experienced in the leadup to the death of his son, Kobe.

Ngannou revealed his son had mild inflammation of the brain ... which led to him fainting twice. The first incident happened while they were in Cameroon, but he said the doctors found nothing.

The second incident occurred in Saudi Arabia. He said while they didn't perform a scan or an MRI ... the doctors believed Kobe had a swollen lung -- which was pressing against his chest and preventing him from breathing. They gave him some medicine and said that he would be OK.

Francis said he "put his guard down" after that, believing the doctors were able to diagnose the problem.

The former UFC heavyweight champion then found himself in Dubai -- although it's unclear how much time passed between those events. That's when he said he learned of Kobe's death.

"My phone rang; it was my little brother, saying, 'Bro, things are not going well here,'" Ngannou said. "He said Kobe passed out. He's not breathing, we are at the hospital, they kicked me out from the room."

After getting disconnected ... Francis called back to try to get more information. While speaking with his brother, a nurse came out and broke the news of his son's passing while he was on the other line.

While Ngannou has gone through an unspeakable tragedy, he said he finds peace in knowing he'll see his son again soon.