The pregnant author, 30, shared a heartfelt Instagram tribute to Shriver, 64, on Mother's Day Sunday, sharing numerous photos of the mother-daughter duo throughout the past three decades.
The heartfelt post also includes images of Shriver's daughter Christina, 28, and sons Patrick, 26, and Christopher, 22, all of whom she shares with ex Arnold Schwarzenegger.
"Happy Mother’s Day to the greatest and most remarkable Mama in the entire world!" Schwarzenegger Pratt wrote. "We are the luckiest 4 kids in the entire world to have you as our mama. I am so beyond blessed to learn from you and you have made me want to be a mama for as long as I can remember."
"You mother not only us 4, but everyone you come in contact with," the mom-to-be added. "You are the Queen mother to all and I am so lucky to have you as my mom. I love you! ♥️."
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Last month, PEOPLE confirmed that Schwarzenegger Pratt is expecting her first child with husband Chris Pratt. This will be the second child for Pratt, who shares 7½-year-old son Jack with ex Anna Faris.
"Katherine is getting more excited every day,” a source previously told PEOPLE, adding that she “is starting to add items to a baby registry.”
Related: Chris Pratt Crashed Wife Katherine's Baking Video
Although the couple isn’t able to gather with their loved ones at present due to the coronavirus pandemic, Schwarzenegger Pratt’s pals are still hoping to celebrate the new baby.
“[They would love] to have a shower [for Katherine] before the baby arrives,” the source added. “She really wants to celebrate with her friends and family [if it becomes possible].”
While recently speaking with his wife’s family for a #HomeTogether Instagram Live chat, Pratt, 40, packed on the praise for his mother-in-law Maria and brother-in-law Patrick.
"I really love what you're doing,” the Guardians of the Galaxy star told Shriver and Patrick. “This is really fun, and being right here, right now, it's just uncanny, you guys are both just so beautiful. I'm so lucky to have married into such a gorgeous family."
"You're gonna have another beautiful family member," Shriver replied.
And the day before Mother's Day, Pratt made a cute cameo in his pregnant wife's Instagram Live, during which she was baking a cake. Joking that he's working as her camera operator while fixing her tripod, the dad of one shared a laugh with Schwarzenegger Pratt before giving her a sweet kiss.