Fans went wild for the photo and shared their delight in the comments section.
"Gorgeous family pic," one remarked.
"YAY! All together," exclaimed another.
"They got the navy shirt memo," a third joked.
The Chilean-born actress and model shares her second son Lennox Miller with ex-husband and AFL player Brad Miller.
"When Isaiah was in prep, most of the other mums thought I was the nanny. Most people are quite shocked to find out I'm a mum, and then they find out I've got two kids and they're like, 'Oh my gosh'," she has previously explained to the Daily Telegraph of starting her family from a young age.
Pia and Patrick announced their engagement in November 2020 and in a chat with Daily Mail Australia, 77 Diamonds managing director Tobias Kormind revealed the eye-watering estimated cost of her stunning engagement ring.
“From Pia Miller's celebratory Instagram post, her ring looks like a 10 carat to 12-carat solitaire oval diamond, set in a platinum band, which would be priced at between US$800,000 (AU$1.10million) to US$1.4million (AU$1.9million),” Mr Kormind said.
Patrick, 56, is the CEO of Hollywood talent agency WME (who represents the likes of Matt Damon) and is estimated to be worth US$440million (AU$630million).
To mark his recent February birthday, Pia shared a loving tribute to her future husband.
Alongside a candid black and white photo of smiling Patrick behind the wheel of a car, the mum-of-two penned: "Celebrating you today & always 🤍 Feliz cumpleaños mi amor."