Duhon said in a tweet Sunday that he had filed for divorce from Downs prior to her allegations this month that he cheated.
"Prior to any statements made about me, we were no longer living together and I already filed for divorce," the reality star wrote.
"This was known by both parties, my lawyer, and the lawyer for the show."
"The reason that led me to filed for divorce from Ms. Downs was thoroughly understood by all parties as well," he added.
"Infidelity was not a reason, nor did I ever admit such a thing. Thank you to those of you who have shown support throughout this tough time."
Downs said in a tweet Nov. 5 that she "just got a call from the woman who's sleeping with my husband" and that Duhon had admitted to cheating.
She responded to Duhon's denial of infidelity in a lengthy post Sunday.
"I see that instead of finally operating in integrity, @Nate_MAFS chose to continue to lie. My husband & I had problems. Yes. He was dishonest and there were women throughout our ENTIRE marriage," the star claimed.
"I can proudly sat that even on our worst day, I honored my vows and loved my husband," she added.
"His infidelity and abandonment of the marriage released me. And although I'm not excited about the impending divorce, I am proud of this women who know what she deserves and a God who has shown me the true definition of unconditional love."
Duhon and Downs met and married in Season 5 of "Married at First Sight," a Lifetime series that pairs couples who have agreed to wed after they first meet.
The series will return for a sixth season in January.
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