Kylie Jenner Boards Private Plane With Wedding Dress

Kylie Jenner just boarded a private plane to her birthday yacht party with a very interesting piece of luggage ... a garment that certainly looks like a WEDDING DRESS ... but TMZ knows otherwise.

Check out this pic from the tarmac Tuesday afternoon at the Van Nuys Airport ... there's a flowing, feathery, white dress protruding out the bottom of a garment bag as it's loaded into the plane. In the worker's other hand -- what appears to be a suit ... possibly a tux.

Don't cue the wedding bells just yet though ... several of our Kardashian-Jenner sources tell us Kylie's NOT walking down the aisle with Travis Scott.

Fact is ... Kylie is notorious for messing with people, and it seems odd she would leave the train to her wedding dress exposed, knowing full well there are paparazzi watching.

What's more ... multiple Kardashian-connected sources tell us, she's not getting married on the trip.

As we first reported ... Kylie is jetting off to Italy begin her 22nd birthday celebration, which is going down on the $250 million mega-yacht, "Tranquility."

Kylie boarded the plane with Travis and their baby Stormi, plus Kris Jenner, Scott Disick, Sofia Richie and Corey Gamble ... as well as her assistant, Victoria, and her friends Stassi Karanikolaou and Yris Palmer.

Noticeably absent on the flight -- Caitlyn Jenner and all of Kylie's sisters. Of course, Kourtney's been vacationing in Europe, and it seems she'll join the party at some point.

One source says it's definitely NOT a wedding because Kim and Khloe are not going to join on the trip.

You could argue ... Travis set the stage when he gifted Kylie a garden of rose petals Monday, covering the floor of her mansion. Travis wrote, "We're just getting started." She also got a $21,000 custom floral arrangement from La Fleur Bouquets inspired by the Kaws x Dior collab from her best friend Yris Palmer.

FYI ... Kylie and Travis have been together for a little over 2 years. Marriage is certainly in the cards ... just not on this trip, we're told.

Stay tuned ...