Michelle Williams quietly welcomes baby No. 4, her third with husband Thomas Kail

Michelle Williams and her husband, Thomas Kail, have grown their brood, Page Six can confirm.

The couple quietly welcomed a baby via surrogate six weeks ago, People first reported Thursday, making the actress a fourth-time mom and the director-producer a third-time dad.

“They couldn’t be happier to expand their family, and Matilda has been doting on her younger siblings,” a source told the magazine, referring to Williams’ 19-year-old daughter, whom she shared with late actor Heath Ledger.

The family reportedly has been spotted around their New York neighborhood with the new addition in tow.

Reps for Williams did not immediately respond to Page Six’s request for comment. Reps for Kail also were not readily available.

Williams, 44, and Kail, 48, are also parents to 4-year-old son Hart and a 2-year-old whose name and sex they have not disclosed.

The pair met when Kail directed and produced “Fosse/Verdon,” which won Williams the 2019 Primetime Emmy Award for outstanding lead actress in a limited or anthology series or movie.

After she was spotted buying baby clothes in London in December of that year, People confirmed she was both pregnant and engaged to the “Hamilton” director.

The outlet further noted that Matilda played matchmaker for the lovebirds.

“Michelle fell in love,” a source explained at the time. “She is happy and fulfilled and ready for another child.”

The duo made their first official public appearance together at the 2020 Golden Globes Awards, where Williams won best performance by an actress in a miniseries or motion picture made for television for “Fosse/Verdon.”

Two months later, she and Kail were photographed sporting apparent wedding bands, and Hart was born in June.

The “Brokeback Mountain” star gave birth to her and the “In the Heights” director’s second child together in October 2022.

The following January, Williams spoke candidly about the struggle of being a working mom.

“We have to stay in the workforce, even though it often feels like it’s untenable,” she shared with Entertainment Weekly at the time.

“My heart obviously belongs to my children; they tug at it the most. But I really want to be able to have both. And I think that it requires deep thought and learning and the support of other women to figure out how to get through it.”

Williams was previously married to musician Phil Elverum, and Kail’s first wife was actress Angela Christian.