"Happy Mother’s Day to the greatest and most remarkable Mama in the entire world! We are the luckiest 4 kids in the entire world to have you as our mama," she wrote of her three siblings, Christina, 28, Patrick, 26, and Christoper, 22, whom Maria shares with Arnold Schwarzenegger.
"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," Katherine continued. "You mother not only us 4, but everyone you come in contact with. You are the Queen mother to all and I am so lucky to have you as my mom. I love you!"