Katherine Schwarzenegger shares rare family photos with husband Chris Pratt

Katherine Schwarzenegger marked a family milestone this weekend: her father Arnold Schwarzenegger's 78th birthday.

The author, 35, took to Instagram with some moments with her husband Chriss Pratt at her father's birthday celebrations.

The slideshow featured photos of her with her sister, Christina, 34, as well as of her husband, Pratt, posing with the Terminator actor.

Another snap was of Katherine with one of her daughters named Lyla, 5, and Eloise, 3. The couple also shares a 9-month-old son, Ford.

Her post wrapped with a lighthearted video clip capturing the Schwarzenegger siblings as they geared up to surprise their dad. In the clip, Katherine addressed the camera, “Today, we’re going to be celebrating our dad’s birthday,” while her brother Patrick, 31, chimed in with, “Follow us.”

Christina followed behind with a birthday cake in hand before the video cut to an outdoor party setup filled with family cheer.

Patrick, 31, then smiled and said, "Follow us," as Christina trailed behind her siblings, carrying a cake with lit candles. The video ends with a quick glimpse of a lively outdoor party setup.

"Leo Season," Katherine captioned the post.

Just days earlier, the mother-of-three teased another big family milestone to come. "It just hit me that we’re 3 months away from having a one year old in the house… MY BABY!" she wrote over a photo of herself holding son Ford.