Kris Humphries can breathe a sigh of relief -- his ex-girlfriend Myla Sinanajinsists she's NOT PREGNANT ... her belly's just naturally round.

Myla was out in Jersey earlier today, where a photog asked her straight -- are you pregnant or not? Myla responded, "I am definitely not pregnant."

What Myla DOESN'T explain is why she texted her lawyer Friday night that she WAS pregnant -- and why she told numerous other people, including Kris, that she was expecting.

Myla's latest version is that people just started talking and, "Of course, me not being a size zero kept it going."

That, and her lying about being pregnant.

From TMZ.com

Picture/Thumbnail via AceShowbiz.com