The big event was held at Katherine's mother Maria Shriver's Los Angeles home, per E! News.
Maria played host to 100 attendees, one of which described the shower as "beautiful and elegant."
Katherine "looked stunning in a white skirt and fitted tank top with beaded fringe. Her hair was clipped back on one side," according to E!'s source.
Other juicy details from the soiree included it being a "backyard luncheon" with live music from a guitar player, lots of champagne and sentimental speeches from her friends and mother.
Chris, 39, arrived at the shower around 2 p.m. after it had been going on for a while. "Maria introduced him over the microphone as Katherine's husband to be and future fiancé. Everyone cheered and whistled," the source said.
They finally made their red carpet debut on Monday, April 22 at the Avengers: Endgame premiere in Los Angeles.