Michelle Williams Welcomes Third Baby With Husband Thomas Kail

Michelle Williams and her director husband Thomas Kail are expanding their family ... welcoming their third child together.

The actress recently welcomed a baby via surrogate, and the child is about 6 weeks old now ... according to PEOPLE.

Michelle is now a mother of four ... her oldest is 18-year-old daughter Matilda, whose father is the late 'Dark Knight' star Heath Ledger.

With Thomas, Michelle shares a 4-year-old son, Hart, and another child born in 2022 whose name and gender have not yet been revealed. Michelle and Thomas have not announced the name or sex for their youngest child either.

If you're wondering why it took six weeks for the media to catch wind of Michelle's baby, consider this ... she's got a new TV series launching on Hulu tomorrow, "Dying For Sex."