The 7 Biggest Surprises of Ariana Grande's Honeymoon Tour in Los Angeles

She's been compared to some of the greatest female powerhouse vocalists including Mariah Carey and Celine Dion.

So it's no surprise that when you hear Ariana Grande live in concert, her pipes are on point. (Unlike so many other singers, who will remain nameless, the 21-year-old does not lip sync when she’s performing live.) Grande's April 8th concert at the Forum in Los Angeles, complete with an opening act from a cute British band named Rixton, not only showed off her vocal range -- but was also filled with seven sweet surprises.

NEWS: What You Need to Know About Ariana Grande's Opening Act: Rixton 

ETonline had eyes and ears at the show, and we’re breaking down the best moments from Wednesday's show.

1.  Justin Bieber performed.

The "As Long As You Love Me" singer surprised the audience at Ariana Grande's Miami show on March 28, but on Wednesday, he got really close to her. Bieber, 21, wrapped his hands around her waist and maybe got a little too close to Big Sean's girlfriend.

It definitely looked like they were having a blast performing each other's songs as duets together! Perhaps they'll even do a song together on Bieber's new upcoming album?

The duo sang Grande's "Love Me Harder" together before Bieber went solo on his new track, "Where Are You Now." But they didn't stop there! The crowd that consisted mainly of teen girls went wild as Grande and Bieber joined forces on "As Long as You Love Me."

At the end of the night, Bieber tweeted out a thank you. “Love the stage. Thanks for having me @ArianaGrande and thanks LA. Gotta tour again soon," he wrote.

WATCH: Is Big Sean Picking a Fight with Justin Bieber?

2.  Pop super-producer David Foster played the piano.

Foster has produced for the likes of Christina Aguilera, Celine Dion and Madonna, to name a few. Grande introduced him to the stage calling him "one of the most incredible songwriters of all time" and admitted she was nervous to perform with him.

He played the piano as she beautifully sang the late Whitney Houston's, "I Have Nothing" and showed off her vocal range. This was her defining moment of the night -- the one where people looked at each other and said out loud, "this girl can sing."

3.  Grande proved that girlie-girls have more fun!

Throughout the show, we got a sense of her style and her love for not only "Pink Champagne," but for all things pink. The rosey hue appeared on the stage background, changing from smoke, to clouds, and even pink lightning! And honestly, after seeing Grande's uber-sparkly costumes, we are considering buying stock in glitter!

4.  Her cat ears were tech-savvy! (And she is definitely business-savvy.)

As any fan worth their salt (er, glitter) knows, those cat ears have become a part of her regular wardrobe. But the ones sold to fans for $40 don’t just light up on their own, they actually stay in sync during the show via remote control. After fans download Grande's app and scan a barcode, those kitty ears would glow and light up all night! Now that's a smart business move by Ms. Grande -- not only is this a merchandise sale, but she’s scoring major app downloads at each show.

5.  Her stage falls make way more sense now.

We've all seen those viral stage fall videos, but what you're not seeing are her sky-high heels. The fact that Grande could dance so well and run around the stage in those black boots and sparkly stilettos was already super impressive!

Without heels, Grande measures 5 feet tall.

6.  Bring on the male dancers.

Unlike many female artists with backup female dancers, Grande's male-to-female dancer ratio was about seven guys to three girls. At any given time, she had a group of attractive men dancing behind her or holding her up. (Not a bad gig.)

NEWS: Ariana Grande Says She Almost Died the Opening Night of Her Tour

7.  Not-so-surprising: the audience wanted to be just like her.

Call them groupies or just fans, but these girls want to look exactly like their idol. From the half-up ponies to cat ears and short skirts, Grande had countless mini-mes in the audience. They screamed, they cried, they knew every word to her songs. No one sat down, even though they had seats. It was truly an experience to just be in the audience. As Jake from Rixton told ETonline about her tour, "It's just incredible. We walk out every night, and the arena is absolutely packed. Everyone is joining in. Her fans have been so lovely to us."

It's no wonder that at the end of the show, Grande sends tweets like this one saying, "Love u babes the most. You just can't imagine."

Check out the video below to see what Grande has to say about her diva behavior.