Sources told People that Pratt, 39, was among many of the celebrity guests at the party, held at Schwarzenegger's mother Maria Shriver's home. Another star in attendance was Oprah Winfrey and Katherine's father, "Terminator" star Arnold Schwarzenegger, who came after attending son Joseph Baena's graduation.
Witnesses say Katherine, 29, wore a white dress for the soiree, and that the home was decorated with white candles and flowers. Live music reportedly played in the background for the shower.
The low-key celebration is likely reflective of the low-key couple's future wedding, a source told the magazine.
“Chris and Katherine’s wedding will be a very intimate affair with just their closest loved ones,” an insider said. “They don’t want it to be a circus. The focus will be their commitment to each other, and God will play a very large role on their big day. It’s been such a special time not just for them, but also for their families. Everyone is so excited.”
Pratt, 39, announced his engagement to the author in January after dating for just seven months.
“Sweet Katherine, so happy you said yes! I’m thrilled to be marrying you," Pratt wrote on Instagram at the time. "Proud to live boldly in faith with you. Here we go!”
“I think that, you know, for me my family is very involved. I'm very involved, [Chris is] very involved so it's a great combination of everything and just a really exciting and fun [time],” she gushed.