'Jersey Shore' Stars Announce Engagements, Sammi's Is Real But Not Vinny's

"Jersey Shore" stars Sammi Giancola and Vinny Guadagnino's dueling engagement announcements on April 1 were not a part of a prank war ... well, not entirely.

Sammi Sweetheart's engagement to boyfriend Justin May did, in fact, happen ... as the MTV personality assured her followers her relationship update was not an April Fools' Day joke. She says Justin popped the question on March 16, but they made the risky decision to share the news -- and first photos of the diamond ring -- on April 1.

Her costars offered up some sincere reactions ... as Jenni "JWoww" Farley, Mike "The Situation" Sorrentino, Angelina Pivarnick and Pauly "DJ Pauly D" DelVecchio all shared their congratulations in the comments section.

We can't blame "Jersey Shore" fans for having doubts, however.

Sammi's costar Vinny also notably announced his engagement on Monday -- but his proposal was all a prank. ICYMI, VG shared a photo of himself down on one knee popping the question to an unidentified woman.

In the background of the upload, massive light-up letters spelled out the question, "Marry Me?"

While countless fans were quick to call out the proposal as a joke, thousands hit the like button, thinking Vinny was really heading to the wedding altar.

As April Fools' Day came to a close, Vinny confirmed the life update was merely a prank ... but called out the 300K followers who showed love for the proposal news.

He added ... "Damn 300K on the April Fools joke. Y'all really wanted me to get married."

Vinny has since wiped the prank from his Instagram page, seemingly confirming his bachelor status. April prank champ??? We'd say so.