During Lauren and Whitney’s Season 3 work trip to the French capital, Emily In Paris’ Lily Collins made a brief, but très chic appearance as a model at the annual Crillion Ball.

Lauren's first major task as a Teen Vogue intern was to work at the Young Hollywood Party. Most fans remember this episode as the time Lauren got in trouble for sneaking Heidi and Audrina inside, but it was much bigger than that. "That's hot" era Paris Hilton was in attendance, which was a pretty big deal.

Paris Hilton's then-nemesis Nicole Richie was at that same party.

The movie Mean Girls was released just two years before this 2006 party, making Jonathan Bennett one of the most sought-after guests at the event.

Before she became a cast member on Southern Charm, Landon Clemonts worked at Bolthouse Productions with Heidi as "Brent's other assistant," and she was totally fine taking a back seat on the show. In 2016, the Southern Charm alum told Page Six, "I wasn't on the show that much because, at the time, I really wanted to build my career."

Aside from that, she claimed, "They wanted me to go after so-and-so’s boyfriend and all this. That's not me." But whose boyfriend though?

Lauren hopped on a red eye flight from Los Angeles to New York City so she could deliver a dress to her boss Lisa Love for the Marc by Marc Jacobs fashion show. As a new intern, she didn't get any perks, like staying for the actual show, but Vogue editor Anna Wintour was sitting in the front row. With sunglasses on indoors. What. A. Legend.

Lauren and Whitney were in charge of casting guys their age for a swimwear photoshoot in Teen Vogue. One of the men at the casting was Tom Sandoval, who of course now stars on another legendary reality show: Vanderpump Rules.

It was a stressful situation when Lauren and Whitney worked the Ashley Paige fashion show. However, everyone else in attendance had fun, including America's Next Top Model winner and current Real Housewives of Atlanta cast member Eva Marcille, who was among the guests.

This episode blessed The Hills fans with one of the most historic moments in the show's history: Whitney falling down the stairs during a live segment on Good Morning America. André Leon Talley, the former editor-at-large for Vogue, is the one who decided that Whitney was model material. As complimentary as that is, Whitney probably wishes he never asked her to model dresses on live television.

During a Teen Vogue assignment in New York, Lauren was asked to help at Marc Jacobs, since he was her favorite designer. To her surprise, the man behind the brand showed up and introduced himself while she was alphabetizing inventory. Oh, the glamour.

The Hills started out with Teen Vogue's Young Hollywood Party and continued the tradition throughout the series. During Season 3, the party was off to such a fashionably late start that even Emmy Rosum was in the crowd waiting to get inside.

At least Emmy Rosum wasn't the only one stuck in a line. Hayden Panettiere was in the same predicament at the Young Hollywood Party.

This super close-up moment is of a baby-faced Selena Gomez. Yes, she had a blue streak in her hair, but it was 2007. Give her a break.

After all of the logistical problems at the Young Hollywood Party got sorted out, they were waiting on one thing: Hilary Duff's arrival. As soon she showed up and got seated, the fashion show began.

There was a lot of drama at the Declare Yourself party. Heidi and Lauren were both "coincidentally" invited by their bosses to attend, which was extremely awkward, and the understandable focus of the episode. However, eagle-eyed viewers spotted Justin Timberlake walking into that same event. If only he chimed in on the Lauren vs. Heidi tension.

When Audrina worked at Epic Records, she spent the day with Sean Kingston, an artist signed to the label, while he rehearsed, did a soundtrack, and ultimately performed on Jimmy Kimmel Live!

Whitney styled then-budding artist Lady Gaga for a big performance. However, the singer's zipper got stuck and she was in a panic. That's when Lauren stepped in and saved the day. Yes, Lauren actually got to assist Lady Gaga with a wardrobe malfunction, and in return, Gaga called her her hero.

Stephanie Pratt went on a secret date with Lauren's former flame Doug Reinhart. Well, as secret as a filmed interaction can be. However, Brody's mom Linda Thompson spotted them and came over to say hi. She was out with her good friend and Real Housewives of Beverly Hills OG Taylor Armstrong.

Brandy consulted Audrina and her coworker Chiara Kramer on which photo she should use for an album cover while they were at the recording studio. Unfortunately, Brandy did not return the favor and weigh in on Audrina's ups and downs with Justin Bobby Brescia.

During Season 5, Spencer spent a lot of time with Stacie the bartender, and her friends. He asked them what song it would take to get them dancing on the bar and Scheana responded with Def Leppard's "Pour Some Sugar On Me," but the bar-top dancing did not actually happen.

The White Tie Affair went out with Audrina and Stephanie for a night out. After a lot of flirting, the bassist revealed to Stephanie that he has a live-in girlfriend back home, and she didn't waste any time getting out of there.

There's no storyline to this one. Tom Green just happened to be at one of Heidi's work events.

Singer Ryan Cabrera briefly dated Audrina and appeared during several Season 6 episodes. It all came to head when Audrina started crying and left one of his concerts... and went back to Justin Bobby, of course.

Another season, another Young Hollywood Party. This time Nylon hosted the event, which meant the cast members got to attend as guests instead of employees alongside Kanye West-era Amber Rose, futuristic shades and all.

90210 cast member Shenae Grimes attended Nylon's Young Hollywood Party along with the cast members.

This scene went down while the cast filmed Season 3, but it did not make the cut. Kim Kardashian attended Heidi and Spencer's housewarming party along with (ex?)-stepbrother Brody Jenner. This did not make it into the show's original run, but it was a part of the unaired footage during The Hills 10-Year Anniversary Special, which aired in 2016. Just imagine if Kim was a part of The Hills. That really would have changed the reality TV landscape.

There was plenty of drama on The Hills to keep fans entertained, but wondering which famous faces might pop up in the next scene was always such an exciting part of watching. Now, the show's stars are celebrities in their own right, but back then, viewers tracked the celeb cameo appearances just as much as Spencer's changing facial hair.