Olivia Munn Says Her Son ‘Made Me Stronger’ in Sweet Birthday Tribute: ‘Magic Malc Turns 3 Today’

"You cracked my heart wide open," the mother of two wrote on Instagram about Malcolm

Olivia Munn’s baby boy Malcolm is now 3!

On Sunday, Nov. 24, the mother of two, 44, posted a cute tribute on Instagram to celebrate her son's birthday. She shares the boy with husband John Mulaney, 42.

The post featured a mirror selfie, in which she is wearing a white robe and stylish tortoise frames as her son is perched on the marble countertop.

"Magic Malc turns 3 today," Munn wrote in the post's caption, which also revealed that the photo was captured during a sensitive moment in her life.

"This photo was taken last year just around the time I found out I had breast cancer," she continued. "I remember this time fondly all because of this little boy."

Related: John Mulaney Shares Son Malcolm's First Reaction to His Baby Sister: 'He Thought She Might Be a Toy' (Exclusive)

Munn added, "He’s made me stronger and softer in ways I never knew I could be. Happiest Birthday my sweet boy. You cracked my heart wide open."

Malcolm has a younger sister, Méi June Mulaney, who was born in September – just two months after Munn and Mulaney tied the knot in an intimate ceremony.

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Malcolm made his Instagram debut in December 2021 when the proud parents each shared sleepy snaps of him on Christmas Eve.

"Meet Malcolm Hiệp Mulaney," Mulaney wrote at the time. "He has his whole life ahead of him. He hasn't even tried seltzer yet. I'm very in love with him and his whole deal. Happy Holidays."

Munn told PEOPLE in April about how her son kept her spirits high amid her breast cancer battle in 2023.

"When I’m with him, it’s the only time my brain doesn’t think about being sick," she said. "I’m just so happy with him. And it puts a lot of stuff into perspective. Because if my body changes, I’m still his mom. If I have hot flashes, I’m still his mom. If I lose my hair, I’m still his mom. That’s really what matters the most to me. I get to be here for him."