One of the biggest curveballs in this year's Rock the Garden lineup was the announcement of St. Paul's futuristic-R&B quartet thestand4rd, who will kick off the festival on Saturday, June 20 at the Walker Art Center.

If you said Who? or simply want to know more about this skyrocketing group, here are four quick facts about the four young men in thestand4rd (pronounced "the standard"):

1. They will be the youngest act to play Rock the Garden

Having recorded "Without You" and becoming a YouTube sensation when he was only 15 years old, the artist formerly known as Spooky Black, Corbin Smidzik, is now 16. Though his bandmates are slightly older, the remaining three are still in their early 20s—Allan Kingdom just celebrated his 21st birthday and Psymun, the group's oldest, is 22.

2. They already have a huge following outside of Minnesota

Spooky Black's lo-fi video for his creeping single "Without You" took off like wildfire. Within weeks of the video's debut, the do-rag clad young artist was hailed by Complex as a "Caucasian sensation" and written up on hip-hop blogs around the world. No one was quite sure what to make of the kid, who wandered through the video dressed in '90s-R&B era turtlenecks and gold chains, and his name was downright cringeworthy. But one thing was for certain: the little dude could sing.

To put Spooky Black's popularity into perspective, he was so fascinating to music critics around the country last fall that the New York Times' pop critic Jon Caramanica was front and center at thestand4rd's debut performance in New York City to report on how the young artist sounded live.

Spooky Black soon fell in with a crew of like-minded artists from his hometown, teaming up with rapper-on-the-rise Allan Kingdom, MC and crooner Bobby Raps, and otherworldy producer Psymun to form thestand4rd. And the rising tide has raised all four of their ships: each time a new member posts a track, whether as thestand4rd or one of their solo projects, hundreds of thousands of fans rush to stream and like their output on YouTube and Soundcloud.

And now, Allan Kingdom has gained such notoriety for his distinctive brand of staccato, stream-of-conscious rap that he's working with one of the biggest hip-hop stars in the world, Kanye West. Kingdom recently performed with West at the Brit Awards and appears on the rapper's new single, "All Day."

3. Rock the Garden will only be their third show in the Twin Cities

Because of Spooky Black/Corbin's young age and the rising profile of Allan Kingdom, thestand4rd have not had many opportunities to perform as a quartet. The shows they have played so far have been screaming, sold-out affairs, including their debut gig at the Amsterdam Bar and Hall in November and another follow-up gig at the Varsity to mark the end of their short tour. In total, the crew has only performed in the Cities twice and in public six times, and all of their shows so far have sold out. Quite remarkable to think their seventh show ever will be in front of 11,000 people at Rock the Garden.

4. They are at the forefront of a new movement in hip-hop

To call thestand4rd a hip-hop crew doesn't feel quite right, even though two of their members rap. And to call them a soul or R&B group doesn't make sense, either, even though three of them can croon beautifully. One way that thestand4rd sets themselves apart is that they don't follow any of the conventions for one genre or another—they are more like a boy band that's been beamed down from outer space.

Their undulating, syncopated, and stuttering beats combine the familiar feeling of old funk and soul records with more forward-thinking and downright bizarre elements, and they sprinkle in soulful melodies and bars of rap like painters dabbing different colors onto a blank canvas. This is hip-hop that's been completely deconstructed and reassembled into a new shape, and it's a big part of what makes the young crew so exciting.

Thestand4rd kick off Rock the Garden 2015 at the Walker Art Center on Saturday, June 20, along with Lucius, Courtney Barnett, Conor Oberst, and Belle and Sebastian.

See also:

Thestand4rd make their debut to a shrieking sea of teens and tweens

Minnesota Weird: 10 players who pushed boundaries in 2014

Allan Kingdom 101: What to know about the St. Paul rapper attracting international attention

Allan Kingdom performs live in the Current studio