"Phew, I’m literally a COSMO GIRL!! Can’t believe I’m saying that!
Thank you @CosmopolitanUK for this incredible opportunity If I saw a body like mine on this magazine when I was a young girl, it would have changed my life Issue hits stands 8/31! ," she wrote on Twitter.
It's a pretty big deal, and the magazine has received a lot of encouragement and support for their decision.
But of course, there were also people who believe that the decision by Cosmo is "glorifying obesity" and "promoting unhealthy habits".
British TV commentator Piers Morgan even called it "dangerous and misguided".
BUT, Tess doesn't really care about any of the criticism. Instead, she has clapped back at all the haters.
"To everyone saying I’m a burden to the British health care system, I’m american so you don’t have to worry about my fat ass. Worry about what horrible people you are by whining about how me being on the cover of a glossy magazine impacts your small minded life."