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Oops! Justin Bieber Did It Again - With A Little Help From Britney Spears

Justin clearly saved the best for last.

All month long, Justin Bieber has been putting Taylor Swift, Madonna, and all the other major squad leaders of the entertainment world on notice that he too can really bring it when it comes to the celeb roll-out brigade game.

Bieber's been busting out one, two, sometimes three or more celeb pal endorsements a day to promote the countdown to his "What Do You Mean" single release -- which you better belieb he'll be performing live at the 2015 MTV Video Music Awards -- and for the final stretch of teasing, he went straight to the tippy top and got Britney Spears involved.

Yep, that's Brit Brit alright, in all her smooch-lipped glory, standing right in front of a Las Vegas Britney-themed game to remind everyone that she is the queen forever, and ... but, oh right, this is about Justin Bieber right now.

As the sign says, there's only one day left of this ridiculously star-packed campaign, and we cannot wait to finally hear the tune he's been teasing us about for almost 30 days now.

Bieber released a brief preview sample of his lyrics video for "WDYM," writing that fans should "get excited. It's about the music again."