In the 14 years since her dad Heath Ledger died, Matilda has grown up as the only child of her single mum, Michelle Williams.
But after the Dawson's Creek star married Thomas Kail in March 2020 and had her second baby with him just months later, Matilda suddenly found herself in a family of four.
Sources say the 16-year-old shares a "special bond" with 44-year-old director Thomas, who Michelle met when they were working on Fosse/Verdon.
"Matilda lost her dad when she was two, and Heath's family, including his dad Kim, are all in Perth, so she's pretty much grown up without a father figure," says a source.
"Michelle was worried about how Matilda would adjust to having a stepfather and a sibling enter her world within months of each other, but much to everyone's relief, it's gone really well."
Indeed, new pictures of Matilda and Thomas in New York, taken last week, show their easy, warm relationship.
"Matilda and Thomas shared a laugh and seemed very happy in each other's company," says an onlooker.
"She was laden with bags and he seemed to be taking her somewhere, maybe for spring break or a college tour."
A separate source adds, "Matilda is wise beyond her years. As soon as she was old enough to realise she'd lost her dad, she grew up fast. Michelle thinks she's an old soul, just like Heath was. Matilda and Thomas sometimes seem more like good pals than stepfather and stepdaughter."
Before Thomas, Michelle was briefly married to musician Phil Elverum, and had high-profile relationships with actor Jason Segel and director Spike Jonze.
"Matilda was never particularly close to them, but it's different with Thomas," says our source. "He's the closest thing she's had to a dad since Heath, and she's happy with their family life."
In January, sources close to the family revealed to Woman's Day Matilda will return to her Aussie roots when she turns 17 in October.
Heath's parents are said to be elated over the news as they couldn't see their granddaughter in her home state of New York because of strict COVID restrictions.
"With COVID and WA's strict lockdowns, they haven't seen Matilda for more than two years," says a source.
"It's heartbreaking for the Ledgers, they're missing so much. But Matilda is a strong-willed young thing, just like her dad, and she's informed Michelle that she wants to go to Perth.
"Michelle is extremely protective of Matilda and has tried so hard to shelter her from public life, but she has accepted Matilda's wishes."
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