The cast of "Jersey Shore" was back in action last night on MTV -- but one of them looked completely different!

Jwoww surprised fans of the show with a pretty shocking weight loss and different-looking face during the premiere (above) -- and they were vocal about it on Twitter.

One user tweeted "omg jwoww lost alot of weight! she looks weird," another adding "Yea she looked too small! & her face looked really tight."

Most crushing of all was this tweet: "I liked JWoww much better when he played Lord Voldemort."

It wasn't all disses for Jwoww though, with a fan tweeting "Why's everyone saying jwoww looks horrible now!! I think she looks better than ever" ... and another saying "JWOWW looks better every season."

As a comparison, check out a promo shot for Season 4 ... and back in Season 1 in 2009.

What do you think of her new look? Sound off below -- and check out the gallery for more stars with surprising weight losses.

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