7:40 AM PT -- Joshua JUUUST responded in the most hilarious way ... posting the classic Shaggy video, "It wasn't me," and saying he likes his women BBW (a little thicker).

Amir Khan just went nuclear on his wife, accusing her of banging heavyweight champ Anthony Joshua ... after telling the world he's divorcing her.

Khan has been married to model Faryal Makhdoom since 2013, but took to Twitter minutes ago to announce the marriage is OVER.

"So me and the wife Faryal have agreed to split. I'm currently in Dubai. Wish her all the best."

He didn't leave it there, telling the whole world he thinks Faryal is rebounding with Joshua.

"Faryal moved on quick. Always mentioned to me how much she wanted to be with another guy, from all people another boxer @anthonyfjoshua"

Faryal isn't taking the whole thing lying down (lol), and fired off a series of Tweets of her own saying Khan is just a washed up crybaby looking for attention, and the real cheater in the relationship.

"Accusing other boxers just because your boxing career is finished. Man up amir."

"I'm not the one who's been in the papers every month with my pants down 😂 Cheater!"