No need the hypothesize about Lili Reinhart’s new ‘do.
The Riverdale alum showed off her newly-dyed brunette locks on social media as she prepares to film the upcoming adaptation of Ali Hazelwood‘s best-selling book The Love Hypothesis, changing it up from her signature blonde look.
Lili shared a photo of herself on Instagram July 17 holding up the book with her brown hair pulled back into a bun. In the selfie, the 28-year-old wears a lab coat in what appears to be a school lab, which tracks with her character Olive Smith being a biology PhD candidate.
She further showed off her hair transformation over on TikTok, where she took part in the current trend set to PinkPantheress‘ “Illegal,” shaking hands with costar Tom Bateman while wearing jeans and a button-down shirt over a tank top, with her new brunette ‘do still pulled back into a bun.
“third year phd student looking for a fake relationship,” she wrote over herself in the video before writing “hotshot professor who agrees to fake relationship” over Tom, reflecting the story’s plot.
Lili captioned the video, “hello Dr. Adam Carlsen,” the name of her costar’s character.
While Tom will play her love interest in the upcoming project, the Chemical Hearts actress has been leaning on boyfriend Jack Martin for real life hurdles, like being diagnosed with interstitial cystitis, a condition that can cause pain in the bladder and pelvis, per the Mayo Clinic.
“Never in my life could I have gotten through this without my partner,” she wrote on her Instagram Stories in January. “It’s not easy to have a chronically ill girlfriend—when I spent months barely leaving the house, couldn’t walk due to pain, and felt incredibly depressed due to the shift in my quality of life.”
Lili added at the time, “Jack’s love and support has never waivered for a second during a time when my body was truly falling apart.”
A few months earlier, Jack has also helped to through some of her mental health struggles, like by holding her hand through a particularly difficult October 2024 public appearance.
“That’s the ironic thing that people don’t see,” she told Self in an interview published in January. “I’m literally in Washington, D.C., at the White House giving a speech on mental health. And then that same night, I am sobbing, in so much discomfort, and feel so defeated.”
What also helps her is knowing that her visibility could help other women going through similar situations feel seen.
“No one ever knows what that is when I talk about it,” Lili explained. “But my urogyno is telling me so many women have this, and that’s why I think it’s as important as it is to just be like, ‘Hey, I’m dealing with it too.’”
Sami Sheen
The daughter of Charlie Sheen and Denise Richards shared her at-home hair dying journey, including its many missteps, on TikTok and raved about the results.
“I’ve been wanting to do this to my hair for years now,” she said, “and I’m so happy that I finally did it.”
Carrie Underwood
Trading in her signature golden locks, the country music star wrote on Instagram in August 2025, “Well, the last time I saw my natural hair color, I was probably about 12 years old, but I thought it might be time to give it a second chance.”
Jason Momoa
In July 2025, the actor shaved off his beard for the first time in six years to film Dune: Part Three, which required him to rock a clean shaven look to reprise his role of Duncan Idaho.
Kelly Clarkson
The American Idol winner debuted a shorter hairdo in a July 2025 The Voice promo, trading her signature blonde waves for a shorter, darker bob style.
Chris Pratt
The actor debuted a bearded look, which he sports on season two of The Terminal List, in June 2025.
Finn Wolfhard
The Stranger Things star changed up his trademark shaggy hairstyle in May 2025 by debuting a buzzcut at the 2025 Crunchyroll Anime Awards in Tokyo, Japan.
Sebastian Stan
The Marvel actor said goodbye to Bucky Barnes’ signature long hair in April 2025, showing off a shaved head at the Los Angeles premiere of Thunderbolts*.
JoJo Siwa
In March 2025, the “Karma” singer debuted her rainbow mohawk at the GLAAD Media Awards.
Emily Ratajkowski
In a March 2025 TikTok video, the model called this ‘do with shaggy bangs the “worst haircut of my life.”
Gypsy Rose Blanchard
The Gypsy Rose: Life After Lockup star debuted a short bob in March 2025, more than two months after giving birth to her and fiancé Ken Urker‘s first child, daughter Aurora Urker.
Whitney Rose
The formerly blond Real Housewives of Salt Lake City star debuted a red bob on Watch What Happens Live in January 2025.
Hailey Bieber
The model debuted lighter locks in September 2024, a month after giving birth to her and Justin Bieber‘s first baby, son Jack Blues Bieber.
Lily Collins
The Emily in Paris star debuted her dramatic transformation at the world premiere of her new horror movie, MAXXXINE, in June 2024.
“Changing my hair always brings out different sides of my personality and I love playing around,” Lily told Vogue. “This cut and color feels bolder and yet somehow lighter. And completely more me—right now.”
Katie Holmes
While attending Chanel’s Tribeca Film Festival Artists dinner in June 2024, Katie debuted a subtle, yet striking transformation of rich caramel balayage highlights that were blended throughout her brunette tresses.
Kylie Jenner
The Kardashians star debuted a platinum blonde look and a bob haircut after rocking waist-length strands for quite some time.
“Did someone say they missed king kylie,” Kylie teased in the caption of her June 8 Instagram post, to which her sister Khloe Kardashian cheekily replied, “I did! I did!!!!!!”
Lisa Rinna
The former Bravo star debuted a platinum blonde look during 2024 Paris Fashion Week Haute Couture.
Priyanka Chopra
The Heads of State star debuted a drastic haircut—a shoulder-grazing bob—while attending a Bulgari event in Rome i May 2024.
Jessica Biel
In May 2024, the actress chopped her hair into a bob that many fans on social media said reminded them of one of the looks she sported as Mary Camden on the ’90s series 7th Heaven.
Megan Fox
The Transformers actress returned to her dark brown tresses and debuted a sassy bob in May 2024, a month after she dyed her hair blue to enter what she dubbed her “Jedi era.”
Dannielynn Birkhead
At age 17, the daughter of the late Anna Nicole Smith debuted a new lob hairstyle overnight during 2024 Kentucky Derby weekend, which she attended with dad Larry Birkhead.
Demi Lovato
The singer debuted a lighter, shorter ‘do in April 2024.
Kelly Osbourne
The Fashion Police alum debuted a blonde bombshell hair transformation May 8.
Kim Kardashian
Back to blonde: Kim debuted a new platinum ‘do in April 2024.
Rihanna
The Fenty Beauty founder debuted a bright blonde hair transformation April 17 while celebrating her latest Fenty x Puma collection in London.
Delilah Belle Hamlin
The model debuted a bleach blonde pixie cut at the FRAME event April 4.
Megan Fox
The Jennifer’s Body star traded in her bubblegum pink tresses for a baby blue bob, which she debuted April 2.
Zendaya
Less than a month afer chopping her hair into a long bob, Zendaya debuted a honey blonde transformation at the Challengers premiere March 26.
Elle Fanning
The Great star ushered in spring with a fresh cut, as she debuted a long bob March 25.
Rachel McAdams
The Mean Girls alum swapped out her signature blonde hair for a dark brunette transformation on March 18.
Bre Tiesi
The Selling Sunset star looked completely unrecognizable after debuting a dramatic blonde transformation March 16.
