From Paris Hilton to Ashley Benson: 14 stars you forgot were in The O.C.

Disturbing news: The O.C. is officially 20 years old.

On August 5, 2003, the show premiered — introducing the world to Ryan Atwood (Ben McKenzie), Marissa Cooper (Mischa Barton), Summer Roberts (Rachel Bilson), and one of TV's greatest families, the Cohens (Adam Brody, Peter Gallagher, and Kelly Rowan) — and almost instantly became a major part of Millennial culture.

Besides launching the careers of its stars, The O.C. was also the starting point for several familiar faces today and hosted some very random celeb cameos.

Californiiiiiia, here we cooooooome - here are the stars you might not have realised spent some time in Orange County:

Olivia Wilde.

Image: Fox.

Okay, to be fair, who could forget our intro to salad dress extraordinaire, Olivia Wilde? Her inclusion as bad girl Alex, a bartender who dates both Seth and Marissa in season two, was kind of iconic.

Obsessed with the storyline of Alex and Marissa moving in together, and their breakup being the catalyst for Alex deciding to RETURN TO HIGH SCHOOL. Everyone in this show was simultaneously 17 and 30, and I ate it up.

Shailene Woodley.

Image: Fox.

Here's some weird The O.C. lore for you: Shailene Woodley played Marissa's younger sister Kaitlin in season one, but she was replaced by Willa Holland for later seasons because producers wanted to age up the character and Woodley was a late bloomer.

"I was 11 and I was on as a guest, recurring character, or whatever," she told Moviefone in 2011.

"My character went to boarding school and when they decided to bring her back, they actually re-auditioned me to bring her back. But I didn't go through puberty until late: I was the 15-year-old who had no boobs. So, at 11, I was like a little mouse-child. I looked like an eight-year-old. So, there was no weirdness when Willa Holland got it because she was so obviously right for the role and I was so obviously not."

Ashley Benson, Lucy Hale and Janel Parrish.

Image: Fox.

What in the Pretty Little Liars was going on in Orange County?

Before Rosewood, these three PLL alum all appeared in The O.C.: Parrish and Benson even played friends Leah and Riley, in a season four episode. Hale played Hadley, Kaitlin's boarding school roomie in season three.

Chris Pratt.

Image: Fox.

In season four, Chris Pratt played Che, an animal activist whose storylines involve 'getting Summer suspended from Brown' and 'momentarily thinking Seth is his soulmate', all while wearing TV's most ridiculous hat.

Maybe this information will have him sliding up your Hollywood's Best Chris rankings?

Max Greenfield.

Image: Fox.

In an absolute stroke of genius, New Girl and Promising Young Woman star Max Greenfield starred in a season four episode as a YOUNG SANDY COHEN.

All the kudos to the casting team on that one.

What makes this even crazier?

In 2016, Peter Gallagher (Sandy Cohen himself!) played Schmidt's (that's Greenfield's character!) dad in New Girl. Mind blowing.

Paris Hilton.

Image: Fox.

Paris Hilton and Seth Cohen could've been a couple in another version of this show, and I will never not be mourning that possibility.

Hilton played Kate in season one, who meets Seth and Summer at a party for Grady Bridges, the star of The O.C.'s very meta parody of itself, The Valley.

There are so many good moments in this cameo, like when Kate takes a selfie on a flip phone????? And when Summer tells Kate they are from Orange County, she responds: "Orange County? Ew."

George Lucas.

Image: Fox.

Star Wars creator George Lucas played himself - well, a version of himself who was interested in a comic book Seth was working on.

In the episode, after the briefest of work chat, Lucas encourages Seth to attend prom, so Seth runs out of a MEETING WITH GEORGE LUCAS to make it to his school dance.

It's absurd! I love it!

What makes this extra strange is that Lucas has made very, very few cameos throughout his career, and most of them were Star Wars or Indiana Jones related. Creator Josh Schwartz has explained his as a 'shoot for the moon' idea that they managed to pull off, because Lucas' daughter was a huge fan.

Paul Wesley.

Image: Fox.

Before he was a sexy vampire, Paul Wesley guest starred as a bad boy... Crab Shack employee.

In season one, he plays Donnie, who pulls out a gun at a party and gets into a tussle, resulting in him accidentally shooting Luke in the arm.

Jeffrey Dean Morgan.

Image: Fox.

In season two, long before he was involved in Grey's Anatomy's infamous ghost sex scene, or wielding a baseball bat on The Walking Dead, Jeffrey Dean Morgan was an inmate who Sandy visits in prison.

Bella Thorne.

Image: Fox.

Bella Thorne played a young Taylor Townsend in flashbacks during a season four episode, where it's revealed that Summer stole a poem Taylor wrote as a 10-year-old and passed it off as her own.

Nikki Reed.

Image: Fox.

Someone needs to run the data on how many future vampires spent their time in Orange County first.

In season three, Twilight star Nikki Reed played Ryan's love interest Sadie.

Right - anyone else down for a re-watch?

Feature image: Fox.