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"Saved by the Bell" star Tiffani Thiessen stripped down to celebrate her 50th birthday.

On her Instagram page, Thiessen posted a photo of herself sitting in bed, barely covered by a sheet.

"Over the hill," she wrote in the caption, adding the hashtag "thisis50."

Some of her famous friends complimented her bold celebration.

TIFFANI THIESSEN SAYS SHE FEELS 'AT EASE' ABOUT AGING AHEAD OF 50TH BIRTHDAY: 'NOT REALLY GIVING A S---'

Tiffani Thiessen posing covered a sheet in bed

Tiffani Thiessen celebrated her 50th birthday by sharing a stripped-down photo on her social media. (Rebecca Sanabria Photographs)

Jennifer Love Hewitt wrote, "Happy Birthday! I remember knowing you as a teenager and hoping to be as gorgeous as you one day! And I still feel the same! You make 50 look great!"

Sarah Michelle Gellar wrote, "Looks pretty [fire emojis] to me."

Her "Saved by the Bell" co-star Elizabeth Berkley wrote, "Happy birthday beautiful friend!!!!!"

Thiessen turned 50 on Tuesday, but she’s spent some of the past month counting down to the milestone.

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Side by side photo of Tiffani Thiessen in Saved by the Bell and posing covered in a bed sheet

Thiessen wrote "Over the hill" in her photo's caption, adding the hashtag "thisis50." (Getty Images | Rebecca Sanabria Photographs)

Last week, she posted a video and photo of a new tattoo of a butterfly on her hand.

She explained the significance of the symbol in her caption for the post: 

"It was truly special because I have always had a beautiful bond with my grandmother and she loved butterflies. My mom and I both dedicated these tattoos to her. She believed that butterflies symbolize transformation and rebirth and that after she left the human world, she would continue to show us she was with us in this form.

"It also seems fitting as I feel a new sense of transformation as I’m about to turn 50."

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Fox News Digital spoke with Thiessen ahead of her birthday in December, when she revealed she felt more confident than ever.

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Close up of Tiffani Thiessen

Thiessen told Fox News Digital she felt more confident as she approached her 50th birthday. (Axelle/Bauer-Griffin/FilmMagic)

"I don't really know why. I think I have theories on why," she said of her change in perspective. "I think because, you know, in my 30s and my 40s, I felt like a lot of my energy and my time was toward meeting my husband and having children and really putting a lot of effort and time and focus into those people in my life. Where, now that I'm more settled, you know, and I've been married for a while and my kids are a little bit older, I feel like I can put back a little more self time into myself… time for me."

Thiessen is a mother of two to daughter Harper and son Holt with husband Brady Smith. The couple have been married since 2005.

Tiffani Thiessen with her husband Brady Smith and children Harper and Holt

Thiessen and her husband, Brady Smith, have two children, daughter Harper and son Holt.  (Gregg DeGuire/WireImage)

"I just feel a little more… not so fussy about all the stuff that I felt like I was probably a little more fussy about in my 30s and 40s. I don't know. It's kind of like, ‘Here it is,’" Thiessen said ahead of her birthday.

"I'm going to be 50 in a couple of months… and I'm embracing it. I'm really embracing it as best as I could."

TIFFANI THIESSEN'S HUSBAND BRADY SMITH REVEALS SHE MADE THE FIRST MOVE: 'SHE LEANED IN AND LAID ONE ON ME'

Close up of Tiffani Thiessen

The "Saved by the Bell" star said she's "embracing" 50. (Paul Archuleta/Getty Images)

Thiessen focuses on balance when it comes to staying healthy. In addition to her film and TV work, she is a cookbook author and enjoys baking.

"I work out. … I drink lots of water. I try to take care of my body and my mind because I do believe that both go hand in hand with being healthy all over," she said of her routines.

"I want my kids to see that I take care of myself, you know, on the inside and on the outside."

One of her favorite healthy additions has been getting into ice plunging, favored by other celebrities, like Mark Wahlberg and Zac Efron.

Tiffani Thiessen posing for a photo

One of Thiessen's health habits has been ice plunging.  (David Livingston/Getty Images)

Thiessen said she's "gotten very much into that in the last couple of years" and explained that the first time she did it was with her in-laws, who are "in the health business."

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"It was hard," she confessed, "But I was obsessed with how I felt afterward. … It's become extremely popular in the last year, and the health benefits are pretty, pretty amazing with what it can do for you."

Fox News Digital's Emily Trainham and Larry Fink contributed to this report.