Celebrities are officially in their transformation era.

Several stars made major changes to their hairstyles this week, including Kourtney Kardashian, whose time as a platinum blonde came to an end as she returned to her signature dark locks. But she wasn't the only Kardashians star to unveil a new look as her sister Kendall Jenner also showed off highlights that might just inspire you to go lighter for the summer. You know what they say: The sister that dye together, stay together. No one says that? Just us? Cool. 

Plus, Reese Witherspoon soft-launched wispy post-breakup bangs, while Emma Stone also stepped out with a new fringe. And January Jones chopped inches off of her hair in favor of a dramatic pixie cut that her fans went mad for. Finally, Blake Lively was relatable AF when she had absolutely no chill over her husband Ryan Reynold's buff body transformation. 

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

Kourt is back to black.

The Kardashians star's blonde era has come to an end. After rocking platinum strands for three months, she returned to her signature dark hue in dramatic fashion.

Taking to Instagram on May 21, Kourtney unveiled a jet-black look, cheekily captioning her post, "brunette4lyfe."

Who's that girl? 

Zooey shocked fans when she ditched her signature dark brown hair for a feathered blonde 'do. The New Girl star unveiled her dramatic transformation in a series of selfies shared to Instagram May 30.

In the snaps, Zooey had curtain bangs instead of her trademark blunt fringe, prompting her to write in the caption, "who's she?"

What, like rocking bangs is hard? 

Two months after announcing her separation from husband of 11 years Jim Toth, the Legally Blonde star debuted a fresh 'do, unveiling new fringe in a May 23 Instagram post.

In the selfie, which the Oscar winner captioned "I love the South," Reese rocked wispy pieces while posing with a white flower.

Kenny is feeling sunny.

Ahead of the official start of summer, the model lightened her brunette hair, showing off fresh highlights in a May 20 Instagram post shared by her hairstylist Matt Rez.

"sunkissed hair goals," Matt captioned the snap of Kendall's balayaged locks. 

Emma's new look gets an Easy A from us.

The La La Land actress brought back her curtain bangs from the mid-aughts when she attended the Louis Vuitton cruise show in Italy May 24. The Oscar winner's throwback look comes on the heels of her recent bob haircut. 

The heat just got turned up in NYC, but we're not just talking about the temperature. 

When the Deadpool star posted a picture of himself soaking up the city sun in a bicep-baring sleeveless shirt to Instagram Stories May 28, fans couldn't help but notice his chiseled arm muscles. Even his wife Blake Lively couldn't resist sharing the sizzling snap to her own Instagram Stories along with images of a pepper, bottles of Sriracha and a "caution: extra spicy" sign.

We're mad for this transformation.

January took to Instagram on May 27 to unveil her edgy new pixie haircut, posting a selfie showing off her much shorter 'do. The Mad Men star had teased a change was coming the day prior on her Instagram Story, sharing a video of her pet lizard shedding his skin. "Tom and I both shed for the summer," she wrote. "I didn't eat my hair, tho."

In addition to chopping inches off her strands, January ditched her platinum blonde hue for a slightly darker shade.