"OK, so she was getting out of a car just now, and I was literally just alone standing outside of the hotel and I was like, 'I'm not gonna fangirl out,'" she shared with ET when we spoke with her on the red carpet. "Because I get it ... it's a big day today. So, I just stood there and she looked at me and she goes, 'You look beautiful,' and then of course I was like, 'I'm the biggest fan,' and we shook hands. She's amazing."
Billboard Music Awards 2017: Red carpet arrivals
Billboard Music Awards 2017: Red carpet arrivals
Vanessa Hudgens was one of the best-dressed of the night in a nude floor-length number with large bows. So gorgeous!
Is it hot in here?! Lea Michele heated things up -- and showed off her svelte physique -- in this ultra-sexy black dress. She (rightfully) let the outfit do all the talking, sweeping her hair up in a neat bun.
Actress Kate Beckinsale arrives for the 2017 Billboard Music Awards at the T-Mobile Arena on May 21, 2017 in Las Vegas, Nevada. / AFP PHOTO / MARK RALSTON (Photo credit should read MARK RALSTON/AFP/Getty Images)
Hailee Steinfeld, a consistent red-carpet winner, donned a semi-sheer calf-length number over black undergarments. The slicked-back hair and minimal makeup allowed her ensemble to take center stage.
Olivia Munn's sheer black dress, featuring floral appliques, seems conservative at first glance -- but sans bra and (possibly) full-coverage panties, it's definitely a risky ensemble!
He has arrived! Jason Derulo looked dapper in a fancy tux with some teal detailing.
(Photo by Gustavo Caballero/BBMA2017/Getty Images for DCP)
Leggy lady! "Baywatch" star Alexandra Daddario looked incredibly sexy in a dress with a slit that reached all the way above her hip.
(Photo credit should read MARK RALSTON/AFP/Getty Images)
LAS VEGAS, NV - MAY 21: TV personality Rachel Lindsay attends the 2017 Billboard Music Awards at the T-Mobile Arena on May 21, 2017 in Las Vegas, Nevada. (Photo by David Livingston/Getty Images)
LAS VEGAS, NV - MAY 21: DJ Diplo attends the 2017 Billboard Music Awards at T-Mobile Arena on May 21, 2017 in Las Vegas, Nevada. (Photo by Steve Granitz/WireImage)
LAS VEGAS, NV - MAY 21: Actor Sara Foster attends the 2017 Billboard Music Awards at the T-Mobile Arena on May 21, 2017 in Las Vegas, Nevada. (Photo by David Livingston/Getty Images)
Va-va-voom! Camila Cabello embraced her inner Jessica Rabbit with this floor-length red number. Loving the '90s-esque spaghetti straps!
This is definitely.. something. Halsey opted to go shirtless in a classic demi-cup bra -- and then inexplicably went for thigh-high gladiator sandals and a floor-length khaki skirt.
Hot mama! Jessie James Decker's black cutout jumpsuit left little to the imagination -- but she still managed to look classy. And how prom-perfect is her hair?
Stunning! Nicole Scherzinger sent pulses racing in a super-sexy orange ruffled number -- and there's no denying that her figure is slammin'.
Handsome as ever! John Legend wore a double-breasted navy suit over a collared white shirt -- and broke the "don't mix black and blue" rule with black loafers.
Ashley Tisdale is effortlessly stunning in a strapless black wide-leg jumpsuit.
'Bachelorette' Rachel Lindsay is pretty as a picture in a simple black sheath and black strappy stilettos. Someone get her a rose!
Quite the country duo! Billy Ray Cyrus dressed down in light-wash jeans and shades, while wife Tish Cyrus topped off a bright white pantsuit with an unexpected wide-brimmed hat.
Rebecca Black's navy mini is cute as is, but the fun, unexpected pumps give the whole outfit a boost! She's come a long way since her "Friday" days!
Cool BBMA style? It looks something just like this. The Chainsmokers dressed down in camo and denim, but with skinny tailored pants and coiffed hair, they still looked event-appropriate.
All grown up! Noah Cyrus went for black-on-black -- plus ultra-dark locks -- with a lingerie-style bra top and grungy jeans.
Sam Hunt made hearts melt in a clean black tux and smart bowtie.
Hopefully it's not too hot outside! Jason DeRulo's velvet coat looks heavy, but the mint green lapels are admittedly very May-appropriate.
Baby, you're a firework! Kate Beckinsale looks better than ever in a deep-V number seemingly inspired by the Fourth of July.
Jason Kennedy, a total red-carpet pro, wore a perfectly-tailored maroon suit and fresh white sneakers -- an all-around winning look.
The top may be conservative, but Rita Ora bared her whole front and behind in a fishnet-style skirt (or something) that showed off a black thong.
Doing his dad proud! Prince Michael Jackson looked fashion-forward yet comfortable in a black bomber jacket and cropped white jeans.
Musician Lindsey Stirling, a lauded violinist, wore a mixed-media gown adorned with Grecian-inspired gold leaves.
Singer Shawn Hook put a twist on his all-black ensemble with a mustard bomber jacket.
Singer Bebe Rexha kept things classic but sexy in a cleavage-baring black gown.
Mark Cuban knows how to work corporate casual! The "Shark Tank" investor kept things simple in a crisp collared shirt and navy suit.
Whew! We were so distracted by Z LaLa's planet-sized headpiece that we almost didn't notice she went nearly-nude in a dress made of... plastic?
Dapper! Rapper Machine Gun Kelly ditched the boring black suit for a smart blue patterned ensemble -- and worked the classic pointed finger pose for good measure.
Goth meets springtime! Singer Taylor Grey's unique sweetheart-neckline mini was feminine yet rocker-chic.
Chris Daughtry -- possible future 'American Idol' judge! -- wore a perfectly-fitted navy suit with a skinny tie. We think even Simon Cowell would approve.
The sharks have arrived! At first glance, Daymond John's outfit is nothing exciting -- until you notice the baby blue tie and gingham shirt. Ditch the leather jacket, Daymond, we want to see the whole look!
Quite a look! ibley Scoles bared her cleavage and a whole lot of leg in this unexpected gray number.
No fault in this star! Ansel Elgort stuck to black-on-black, finishing off the look with a sleek leather jacket.
Go big or go home! Brandi Cyrus stood out from the crowd in a cerulean suit dotted with stars, which she left unbuttoned over a metallic bra top.
Does he get style inspo from Robin Thicke? Tyler Hubbard of Florida Georgia Line's black and white suit turned heads on the pink carpet -- and while it's a risky look, he seemed pretty confident!
Dang! Jeannie Mai was pink-carpet perfection in a sultry black maxi that showed off a whole lot of leg. (And may we say, those are some toned thighs!)
Major ballerina vibes from Madison Beer's navy dress, which flared out to the knee with layers of tulle. Her pointed-toe heels made her look like a total prima ballerina!
We're getting dizzy -- in a good way! Rachel Platten went all-in on a bold patterned one-sleeved number, toning down the drama with a messy pony.
Here she is...! Miss America 2017 Savvy Shields wasn't wearing her crown, but this sultry red gown was more than enough to prove her title.
Singer Julia Michaels shows off her enviable torso in a strappy bra top, cropped black pants and a bold silk caftan.
Never one to shy away from the cameras, DJ Khaled hammed it up in a shiny blue bomber and bright white kicks.
Social media star Logan Paul played up the skater boy vibes with windswept hair and a bold hoodie.
Hey there! Amanda Cerny's bustier-style top wasn't a traditional choice, but she upped the glamour with long waves and a strappy stiletto.
Actress Laura Marano isn't afraid of mixing things up! She paired her sequinned tulle ankle-brushing skirt with a sheer black crop top.
Wow! If Dencia was looking for attention, she definitely got it in this architectural design. (Hopefully it unzips in the back, because otherwise, bathroom trips aren't going to be fun.)
So on-trend! Singer Whitney Woerz added a black choker to her cutout black jumpsuit -- and rocked a red lip.
Ow ow! Josh Duhamel was every woman's fantasy in this perfectly-fitted maroon suit -- and adorably scruffy facial hair.
Partynextdoor arrives at the 2017 Billboard Music Awards.