Hilary Duff doesn't yet have the Bakers' dozen.

After all, the Lizzie McGuire alum revealed Dec. 12 she's pregnant and expecting her fourth baby, her third with husband Matthew Koma.

"Surprise Surprise!" Duff wrote on Instagram alongside her family holiday card, which read, "So much for silent night" and "Buckle up Buttercups, we're adding one more to this crazy bunch!"

And call us crazy pops, but it was her former Cheaper By the Dozen costar who had the perfect reaction to the news.

"Just 8 more to complete the pack," Alyson Stoner wrote, prompting Duff to reply back, "Ha well played." 

Fans also gave their seal of approval to Stoner's joke, with one user commenting, "THIS WINS THE INTERNET."

Duff and Stoner costarred as sisters Lorraine and Sarah Baker in Shawn Levy's 2003 comedy and its 2005 sequel, which centered on Illinois couple Tom Baker (Steve Martin) and Kate Baker (Bonnie Hunt) and their 12 prankster kids.

And though Duff is expecting her house to get a little more rowdy with the new addition, she probably isn't at risk of having her underwear soaked in meat. 

Rounding out her quarter-dozen are son Luca, 11, who she shares with ex-husband Mike Comrie, and her and Koma's daughters Banks, 5, and Mae, 2. 

Koma is also emotional about growing their clan, writing on social media alongside more photos from the family maternity shoot, "baby #4 is loading..."

In the meantime, Duff couldn't be happier to wake up, wake up with the "Kisses Back" artist.

"Everything is just better with …and because of you," she wrote on Instagram in June, while wishing him a Happy Father's Day. "We love you beyond and thanks for always carrying all the stuff I pack."

To see what Duff and Koma's dreams are made of, read on for this look inside their own Cinderella story:

Back in January 2017, the pair confirmed their budding romance by posing on the red carpet together at Entertainment Weekly's pre-SAG Awards party at Chateau Marmont. 

Shortly after their red carpet debut, a source confirmed to E! News the two had split in March 2017. According to the source, the breakup was triggered by their busy schedules. 

By October 2017, they had rekindled their romance, evidenced by his appearance at her 30th birthday party. "Since Matt got back from tour, they've been seeing each other again," a source told E! News exclusively at the time. "Him being gone on tour was the main reason things didn't work out the first time around, so now that he's back, they picked up right where they left off." As she later revealed on The Talk in December 2017, it was actually the third time they were dating. "Timing is such a big deal… third time's a charm!" she told the co-hosts. 

In June 2018, the couple has sweet news to share: they had a baby girl on the way. "We made a baby girl!" Koma wrote on social media. "She will be as beautiful and sweet as her mother...@hilaryduff another incredible chapter begins."

By the fall, they officially added a new member to the family: daughter Banks Violet Bair. "This little bit has fully stolen our hearts! She joined our world at home on Thursday afternoon and is absolute magic," the actress shared online in October 2018. 

Nearly two years after stepping out publicly for the first time, Koma asked the actress to marry him. 

Duff and Koma said "I do" in Dec. 2019, surrounded by their loved ones! 

When celebrating his one year wedding anniversary to Hilary, Matthew wrote a thoughtful post on Instagram expressing his gratitude for all that she's done during the pandemic. "I'm so in awe of your badassery," he gushed in part. 

Hilary and Matthew went on to welcome daughter Mae James Bair in March 2021.