Nearly 20 years after her parents Amber Portwood and Gary Shirley welcomed her on 16 and Pregnant, the 17-year-old has begun her senior year of high school.

Kristina Shirley, who married Gary in 2015 after his split from Amber, shared a photo of Leah and Emilee, 11—who she shares with Gary—on the first day of the school year.

The 39-year-old captioned her Aug. 13 Instagram post, "First day of SENIOR year and 6th Grade!"

The photo showed Leah wearing a croqueted white sweater with bell sleeves over blue jeans as she posed alongside Emilee, who wore a gray hoodie over a pink tee and jeans for the exciting day. Both girls wore matching hairstyles, with their wavy hair mostly down adorned with a bow.

Naturally, fans couldn't believe that the teenager was already rounding her final year of high school.

"12th grade how is that possible??," one person commented, while another wrote, "Can’t believe our tv niece is this grown up. Please stop growing Leah!"

The milestone moment comes after Leah—who is estranged from Amber—made it clear how she views Kristina, sharing photos from her "coffee date with my mama" on Instagram in July.

She had previously opened up about her decision to cut off communication with her mom due to comments made online.

“Obviously, the past few years, I’ve been feeling a certain way,” Leah shared on Teen Mom: The Next Chapter last year. “But the last straw was when she was doing her lives online to say what she said.”

Indeed, Leah admitted that she couldn’t handle her mother’s online behavior, adding, “She was even talking about me some.”

The high schooler also texted Amber directly on the series, explaining that, while she was "scared" to do so, "the best way for me to forgive her would be me moving on."

"This isn’t meant to hurt you, but I want to let you know that all these years it’s been my decision to not have a relationship with you and nobody has influenced my decision,” Leah wrote in a text during the episode. “I feel like recent online activities have put me in a place where I need to communicate this to put a boundary between us for myself.”

Leah isn't the only celeb offspring to head back to school already. Keep reading for more stars whose kids are in study mode again...

The NBA star escorted his son Prince—who he shares with ex Jordan Craig—ton his first day of fourth grade, joking in an Aug. 12 Instagram, "Man I’m getting old."

The Sabrina the Teenage Witch alum enchanted to see her and husband Mark Wilkerson's sons Braydon and Tucker head back to school on Aug. 12.

"Last first day of school for our Brady," she wrote on Instagram. "Senior year for him and 7th grade for Tucker. May God bless and protect all the children as they head back to school!"

Matthew Stafford's wife snapped this photo of the NFL quarterback sending their twins Chandler and Sawyer off to their first day of fourth grade. As she captioned the photo on Instagram Aug. 12, "New school, same girls."

The former Dancing With the Stars pro waltzed her and husband Sam Cusick's daughters Sage and June to class on Aug. 12, writing on her Instagram Story, “I can’t believe they are both starting school now.”

Summer is winding down. The Whine Down podcaster sent her kids Jolie and Jace—who she shares with ex Mike Caussin—as well as her and husband Allan Russell's son Roman off to their first day of school on Aug. 10.

"First day of Pre-K3, 5th grade & 2nd grade," she captioned a photo of their blended family. "So proud of these three and excited for all this school year will bring."

Jason Aldean's wife shared photos of their kids Navy and Memphis heading back to school on Aug. 11, calling it an "emotional Tuesday."

She's going to school for all the right reasons. The Bachelorette alum saw her daughter Addison start seventh grade on Aug. 11.

"You are incredible Tiny," she wrote on Instagram. "Praying for a great year in middle school!"

The Ex on the Beach alum helped her and Cory Wharton's oldest daughter Mila get ready for elementary school. As she wrote on Instagram Aug. 12, "My little first grader."