Summertime and the transformations are dramatic.

As the temperatures continue to rise, celebrities are heading to their stylists to freshen up their looks and several stars debuted vibrant new hair colors this week. Helen Mirren showed off a bold blue hue while attending the 2023 Cannes Film Festival, while Blake Lively was spotted for the first time with fiery red locks while filming the movie adaptation of It Ends With Us. You know you love it.

Plus, Camila Cabello returned to her "dark and sexy" tresses after sporting highlights for several months and Jennifer Love Hewitt decided to lighten her brunette strands to achieve her dream "summer vibes."

But celebs weren't just changing their hair colors: Stranger Things star Sadie Sink sent fans into the upside down by chopping her red tresses into an edgy mullet and Blac Chyna shaved half of her head to achieve a "mushroom cut." 

Check out the most surprising celeb transformations of the week...

Blake's BFF Taylor Swift isn't the only one feeling burning red.

It Ends With Us fans got their first look at the Gossip Girl alum as the redheaded florist Lily Bloom in the upcoming movie adaptation of Colleen Hoover's bestselling novel. Blake was spotted with scarlet locks on the New York City set on May 15, where she was filming a scene with Justin Baldoni, who's playing her love interest Ryle Kincaid and directing the movie.

The Oscar winner pulled a fast change at the Cannes Film Festival.

Helen debuted a vibrant blue hair color when she attended the opening ceremony and Jeanne du Barry screening on May 16. The Fast X actress paired her dramatic new hue with a matching baby blue gown by Del Core that featured an off-the-shoulder design, a plunging neckline and a ruched bodice attached to a floor-length train. To complete her bold look, Helen held up a black fan with the inscription, "Worth It."

Indeed, she is.

So long, flowing locks. Hello, mullet.

For a forthcoming role, Sadie chopped her signatured red tresses, debuting a bold shaggy cut. Sadie's hairstylist Tommy Buckett took to Instagram May 15 to unveil the Stranger Things star's daring new 'do.  "Sadie," Tommy captioned the photo, which showed off the back of the actress' head. "#sadiesinknewhair."

In an interview with Vogue, Tommy explained that he was aiming for "a cool longer pixie," and admitted he was initially concerned about how Sadie's fans would respond to her new look. 

"When I was doing it," he said, "I was thinking that people are either gonna love me or absolutely hate me."

My oh my!

After rocking caramel highlights for several months, Camila showed off return to her signature dark tresses on Instagram May 15.

"Retro Brunette," Camila's hairstylist Nikki Lee wrote on Instagram of the "Havana" singer's newly dyed locks. "Dark & sexy for summer 2023."

You can't say she half-assed this transformation.

Chyna unveiled a half-shaven head on May 18, ditching the long blonde waves she had been sporting recently in favor of a black pixie cut.

"New cut baby," Chyna captioned a video showing off her bold look on her Instagram Story. "Time to curl." 

Chyna tagged a professional known as Hairstylist of La L.L.C in the clip, with the hairdresser dubbing the model's new style as a "mushroom cut" in their Instagram caption. 

JLH is blonde for the summer.

Several weeks ago, the 9-1-1 star revealed she added highlights to her hair, posting a selfie on Instagram to show off her fresh color. "We did a thing," Jennifer wrote, tagging her hairstylist Nikki Lee. "She's giving summer vibes."

And on May 17, Jennifer shared that she "went even a little bit lighter," adding even more streaks to her brunette locks.