Hilary DuffCredit : Frazer Harrison/Getty Images)

Hilary Duff surprised her fans with a major hair transformation.

The "Lizzie McGuire" star set the bar high as she debuted a head full of wavy cotton candy blue strands alongside clips during the process.

Hilary Duff's Hair Dye: From Blonde to Ultra Bright Blue Color

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She thanked celebrity hairstylists Riawna Capri and Nikki Lee for creating her stunning locks and granting her request amid the late stage in her pregnancy.

Moreover, the "A Cinderella Story" actress also shared why she transitioned from blonde to blue hair. She explained that she just needed some change but took the necessary precaution to ensure that the whole process was safe for her pregnancy.

On the other hand, the former Disney star, who is eight months pregnant, also warned her 16.4 million followers that this is not a baby reveal.

"I swear this doesn't mean I'm having a boy... My mom thought I was trying to tell everyone something! We still don't know who's occupying my apartment- but it's getting the eviction notice soon-ish," Hilary Duff Instagram caption reads, alongside a series of videos and photos showing the behind-the-scenes process.

As for her pregnancy, the 33-year-old actress is tight-lipped about the gender of her third child.

Duff is a mother to a 2-year-old daughter, Banks Violet, whom she shares with husband and musician Matthew Koma, and an 8-year-old son, Luca Cruz, from her previous relationship with Canadian former professional ice hockey player, Mike Comrie.

Read Also: Best Hair Trends As Seen on New York Fashion Week's Autumn/Winter 2021 

The Secret to Hilary Duff's Blue Hair

Her hairstylist managed to reveal the secret behind her vibrant cotton candy blue locks.

To achieve this, Lee explained that they pre-lightened her hair using Joico's Blonde Life and tons of foils.

She then followed it up with a quick pre-tone to eliminate unwanted yellow tone and brassiness before applying the blue dye.

Moreover, Lee went on to detail the "magic formula" that they used with the singer's hair, which they considered the most important step.

They mixed blue and yellow tones and applied the magic formula which is the Joico's Color Intensity True Blue and Mermaid Blue from the roots to the mid-shaft of her hair.

As for the ends of her hair, they added Mermaid Blue with a hint of Peacock Green shade to achieve the gradual blue tones.

The last step would be the deep conditioning treatment using In Common's Crystal Cashmere to seal the hair's moisture.

Fans React Over Hilary Duff's Hair Transformation

Over the comments section, fans and her celebrity friends seem to love her new do.

The "This Is Us" star Mandy Moore praises Duff, saying, "You're the coolest, lady," while actress Alana Materson thinks the blue hair suits her best.

"But it looks so cute!!" she wrote.

Meanwhile, her hairstylist teased her and said, "At least you didn't cut bangs OR GO BROWN (again!). Love you so so so much, and I'm happy to spend the whole day and do it all over again, like, if you happen to have a girl!? do we go pink!??? love you to the moon backkkk!!!."

On the other hand, an individual mentioned that this gave her fans a major throwback during her days as a pop star.

"Popstar Hilary Vibez."

Hilary Duff's Hair Color 2020 

The "So Yesterday" hitmaker is no stranger when it comes to donning fun and vibrant hair colors.

At the start of the quarantine, the former child star joined a slew of celebrities who are dying their locks at home.

At the time, the "Beat of My Heart" songstress took to Instagram as she posted a photo of herself sporting a short blob and blue hair.

In a separate video together with her husband, Koma mentioned that she helped Duff with the coloring process.

"I also dyed her hair. I do a lot of stuff around this house," he said.

The singer-actress donned in this fun hair color for a few weeks before going back to her natural blonde hair.

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