Emma, 28, posted an Instagram photo of her and her aunt, arm in arm.
"Happy birthday aunt @juliaroberts 🎂 you are the queen! I love you 🍰🥂❤️" read the caption.
Among the nearly 4,000 comments was one from Julia herself.
"I love you beyond measure," Julia replied, adding a heart emoji.
Julia also posted on her own Instagram to celebrate the occasion.
"52. Yeehaw. 🎂💃🏼🥳," the caption read.
The comments were full of birthday wishes from Julia's A-list friends.
Singer-actress Rita Wilson also commented, saying, "Happy Birthday! I think you transposed the numbers. It’s 25, right? Love you!!!!"
Emma is currently starring in "American Horror Story: 1984" and Julia was most recently seen in Amazon Prime's "Homecoming."