The 20-year-old model and singer -- whose late father, Michael Jackson, made Culkin her godfather after they were friends during the Home Alone actor's youth -- took to Instagram on Sunday to share a slideshow of flashback snapshots commemorating his special day.
The series of pics included photos of their matching spoon tattoos, which they got last year, as well as a cute pic of them cuddling on a couch while Jackson rocked a pair of bunny ears, and a snapshot of the two of them wearing custom matching plaid overshirts, with "Mack" and "Paris" written on the back.
"Happiest of birthdays mack attack," Jackson wrote in the caption. "I love you so so dearly and keep you very close to my heart. Always."
Culkin -- who is also the godfather to the King of Pop's two sons, Michael "Prince" Jackson Jr., 21, and Prince "Blanket" Jackson II, 16 -- admitted that he's "very protective" toward the Sound Flowers singer during a conversation with Marc Maron on his WTF podcast back in January.
"I'm going to warn you now, I am very protective of her so just look out," the actor said when Maron broached the subject. "I am a very open book when it comes to things but like with her, she is beloved by me."
When asked simply how Paris is doing, the Home Alone star answered, "She’s tall, and beautiful and smart. It’s great."
Check out the video below to hear more from the interview.