Kylie Jenner's Mystery 'Wedding Dress' Revealed on Birthday Getaway

Kylie Jenner ruffled some feathers making people think she was getting married on her birthday trip -- but now, the cat dress is out of the bag ... and it's clear there's no wedding.

The mystery "wedding dress" that was seen being loaded onto Kylie's jet last week made its full debut Saturday on Kylie's Instagram story, where she revealed it was merely a birthday outfit (her 10th so far, apparently). It's a flowing, feathery white gown, nothing more.

Kylie filmed herself getting done up in the dress, and then posted another clip of her running down a hallway in it -- seems like she can move that thing!!!

On the way up to the upper deck of her multi-million dollar yacht, she showed off the garment in all its glory. It's easy to see why some folks thought it actually was a wedding dress -- it's got a train, and looks a lot like something a bride might wear.

As we first told you ... Kylie ain't getting hitched on this trip -- despite the possibly well-planted red herring. Two of her older sisters -- Kim and Khloe -- aren't expected to attend ... and it was suggested to us they wouldn't miss Kylie and Travis' nuptials.

Kris Jenner is there though, as are a bunch of Kylie's closest pals ... plus Travis Scott and baby Stormi too, of course. They're all partying and making the most of Kylie's $250 million rental.