Tess Holliday on the cover of Cosmo. (Picture: Instagram)

The 33-year-old American model - who weighs 300 pounds - has made history by becoming the first ever size 22 supermodel to grace the cover of the glossy fashion magazine, and has hailed the milestone as an "incredible opportunity.

Posting the magazine cover on social media, she wrote: "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! (sic)"

The Cosmo star is the creator of the #effyourbeautystandards Instagram campaign and encourages body positivity on her social media channels which boasts 1.6 million followers on Instagram alone.

The Cosmo star is the creator of the #effyourbeautystandards Instagram campaign. (Picture: Instagram)

Fans of the model took to Twitter to show their support for the cover, one woman said: "How many young women would have been out enjoying life knowing they're beautiful as they are, rather than crying over why they don't look like they "should", if photos like this were more prevalent? (sic)"

Another wrote: "For some reason I burst into tears when I saw this.Maybe because I used to pore through women's magazines at a teen for HOURS of misery, imagining how much happier I'd be if I looked like them. I just pray this means my daughters won't waste so many formative minutes. (sic)"