The Pretty Woman star shared a rare post on Instagram alongside a funny slow-motion video of the duo with party blowers in their mouths and wearing party hats while gazing directly into the camera. The clip ends with Julia and Emma being covered in confetti and bursting into laughter.
WATCH: Julia Roberts shares rare video of niece Emma Roberts in honor of her birthday
Alongside the video, Julia wrote: "Happy Birthday Magical One! Oh, how I love you. #waitforit." Despite Julia limiting the comments, Tom Hanks' wife Rita Wilson wished the American Horror Story star a "Happy happy day," and hundreds of others 'liked' the post.
Emma reshared the video on her own Instagram Stories, captioning it: "Love You!!!"
Julia and Emma share a very close bond. Back in 2013, the Oscar-winner opened up about her relationship with her niece during an interview with Los Angeles Times.
The mother-of-three said: "When Emma comes to stay with us, I always think, 'Please let her be the same,' and she is still the same magical girl she used to be."
Julia and Emma look so alike
Julia added: "I think so much of it has to do with your intentions in taking on a business like this. If you have a pure view of what you want to accomplish, I think you can maintain your sense of self."
It wasn't just her aunt who expressed their love for Emma on her special day, her mother, actress Kelly Cunningham, also took to Instagram and shared a series of photos of herself and her daughter taken over the years.
Emma shared this tranquil photo to mark her birthday
"Happy birthday my love and my force to be reckoned with. You were always up for a challenge and adventure," she gushed.
Feeling the love from her family and fans, Emma took to Instagram to post a stunning photo of herself wearing a red swimsuit while posing on a rocky stream.
"Thank you for the birthday wishes. Feeling very grateful and loved! #31," she wrote in the caption.