Here's the deal ... Britney fans went nuts Friday when her BF, Sam Asghari, posted a picture of a ring on his Instagram story. Eagle-eyed fans pointed out the ring had an inscription reading, "Lioness."

But, Sam is pouring cold water on the speculation he popped the question after more than 4 years of dating ... he says his IG account got hacked and the ring pic was photoshopped.

TMZ broke the story ... Sam went shopping for jewelry earlier this month at Cartier in Beverly Hills, and appeared to be checking out a diamond ring.

Lots of folks took Sam's shopping trip as a signal he and Britney were heading toward an engagement ... because she made it clear back in June at her court hearing she had marriage on the mind.

For now, it seems like people are putting the Cartier before the horse.