Oliver James Montgomery-Bethenny Frankel's Update on Daughter Bryn's Milestone Will Make You Feel Old

Bethenny Frankel's fans watched her endure several days of labor before giving birth to daughter Bryn in 2010.

Now,Oliver James Montgomery more than 14 years later, the Real Housewives of New York City alum's only child is marking a major milestone.

"And just like that… we enter high school," Bethenny wrote on her Instagram Sept. 3. "#daughterlove #highschool #firstdayofschool #whoworeitbest."

The 53-year-old, who documented her pregnancy and arrival of her and ex-husband Jason Hoppy's daughter on RHONY spinoff Bethenny Getting Married in 2010, shared classic first day of school photos with her teen, who wore a black tee, white ruffled skirt, white socks and white and pink Adidas sneakers. Bethenny, meanwhile, sported a floral top and matching pants.

"I remember watching you pregnant!" one user commented on Bethenny's post. "I can’t even believe she’s in high school! Where has the years gone!"

Another person wrote, "High school!!! What?? She was just a baby!!! Where’d the time go??? I feel old, lol!!"

Bethenny also shared a selfie video expressing her excitement about Bryn's new journey.

"It's the first day of high school—ninth grade!" the Skinnygirl founder said. "She still doesn't know what she's doing with her hair, I mean, it's a big day."

She added, "We're already late for school on the first day of high school, new school, ninth grade. We're already late."

The reality star was then seen shouting "Let's go!" as Bryn's voice was heard in the background. Bryn was then shown getting into a car with the family's two little dogs following suit before being called home by Bethanny.

"Oh my god, they don't want her to leave!" she said. "Alright, guys, that's hysterical. Come on guys, we're going in. You're stuck with me."

Read on to see more celeb kids headed back to school this year...

"And just like that…" the Real Housewives of New York City alum wrote on Instagram June 3, alongside photos of herself with daughter Bryn, "we enter high school. #daughterlove #highschool #firstdayofschool #whoworeitbest."

She's got the right stuff! The Lizzie McGuire alum and Matthew Koma's oldest daughter Banks started kindergarten. 

"My queen. My boss. My CEO. My top dog. My big cheese. My kindergartener," Hilary wrote on Instagram Aug. 29. "Let’s go baby girl!!!"

Time flies when you're keeping up with the Kardashians! Case in point: The reality star was having "a really hard time processing the fact" that her daughter True Thompson—who she shares with ex Tristan Thompson—was heading into the first grade. 

"There’s this undeniable feeling that I’m losing parts of who she was with each day that passes," Khloe wrote on Snapchat Aug. 26. “Time moves fast, faster every year it feels like, and this new school year is a reminder to me to fully embrace every moment and soak it all in.”

The country singer and her husband Eric Decker's three older kids—Vivianne, Eric II and Forrest—returned to school on Aug. 19. 

And with baby Denver at home, Jessie wrote on Instagram, "I still can’t believe I have a middle schooler and a 6month old."

Back to school season was off to a shining start for the comedian and Brittany Bell's son Golden Sagon, who started the fourth grade at just 7 years old after skipping kindergarten and pre-K.

Meanwhile, Golden's sister Powerful Queen—who Nick also shares with Brittany—began pre-kindergarten.

As the Good Night, Sister author and her husband Chris Pratt prepare to welcome baby No. 3 together, their daughters Lyla and Eloise headed off to their first day of class.

Katherine captioned this Aug. 18 photo of the girls wearing their custom Stoney Clover backpacks, "How is it already back to school time?!"

Britney Spears' nieces are growing up fast! Maddie—who Jamie Lynn shares with ex Casey Aldridge—began her junior year of high school.

Meanwhile, Ivey—who the Zoey 101 alum shares with husband Jamie Watson—became a first grader.

There's never a right time to say goodbye. That was probably what the "Run It!" singer and Nia Guzman were thinking when daughter Royalty went off to fifth grade on Aug. 27.

The Saved by the Bell alum sent kids Gia, Dominic and Santino off to school on Aug. 20, joking that means he and wife Courtney Lopez "have homework" to do.

"One (and only) year with all 3 kids at the same school," Courtney added in an Instagram post of her own. "So excited to wake up earlier, make lunches they won’t eat and do homework I can’t understand!"

The Teen Mom: The Next Chapter star embarked on not one, but two new chapters when her and ex Corey Simms' twins Aleeah and Aliannah started high school, and her youngest daughter Adalynn—who she shares with ex  Jeremy Calvert—entered middle school.

Backstreet's back to school! The former boybander posed with his and wife Lauren Kitt Carter's three kids Odin, Saoirse and Pearl, writing on Instagram Aug. 23, "Nothing better than watching your children grow and learn."

The HGTV host shared an emotional hug with her oldest son Drake—who she shares with husband Chip Gaines alongside their younger kids Ella, Duke, Emmie and Crew—as he headed back to Baylor University for his sophmore year.

The Buffy the Vampire Slayer alum showed off the back-to-school plaques she made for daughter Charlotte and son Rocky—both of whom she shares with husband Freddie Prinze Jr.—as they began high school and middle school, respectively.

Good luck, Mia! The actress—who played the titular toddler in Good Luck Charlie—started her sophomore year of high school on Aug. 19. 

She quipped on Instagram, "Cue the comments about feeling old."

Teenagers Braydon Wilkerson and Tucker Wilkerson—who the Sabrina the Teenage Witch actress shares with husband Mark Wilkerson—headed off to school on Aug. 7.

She got the boy to his class! The singer was on hand to watch her and ex Mike Caussin's son Jace start kindergarten on Aug. 9.

Meanwhile, the former couple's daughter Jolie began third grade.

The Bachelor Nation star's daughters Kinsley and Charlie started the seventh and fifth grade, respectively.

"I just can’t believe how grown up they are," she wrote on Instagram Aug. 22, "& that they still love to match…& that I still cry on the first day of school no matter how long I’ve been doing this."