“Happy birthday to the best friend, mother, ally, colleague, lover, and partner I could ever wish for,” Culkin wrote, sharing a photo of Song in a bathrobe

Macaulay Culkin in Los Angeles on Oct. 9, 2018; Brenda Song. PHOTO: STEVE GRANITZ/WIREIMAGE; MACAULAY CULKIN/INSTAGRAM

Brenda Song is getting some sweet — and silly! — birthday wishes from fiancé Macaulay Culkin.

On Wednesday, the Party Monster actor posted a tribute to his longtime love on Instagram in honor of her turning 36.

“Happy birthday to the best friend, mother, ally, colleague, lover, and partner I could ever wish for. You are my reason.

I love you,” Culkin, 43, began his caption, first sharing a photo of Song in a bathrobe with a towel around her hair, sitting at a table with a champagne bottle on it.

Macaulay Culkin’s 36th-birthday tribute post to fiancée Brenda Song.MACAULAY CULKIN/INSTAGRAM

The second image in Culkin’s post was zoomed in on the top portion of a milk carton, which displayed a sell-by date of 3/27/2024.

“P. S. The milk is due. Can you pick some up on your way home from work?” he joked.

“😂😂 C’mon Kevin you were so good at grocery shopping 🛒 what happened? ❤,” one fan quipped in the comments, referencing the former child actor’s famous scene in Home Alone.

Culkin and Song met in 2017 in Thailand on the set of Seth Green’s movie Changeland. Culkin later admitted to Esquire that when he and the actress first started dating, he “was waiting for the other shoe to drop,” though he came to realize, “No — sometimes it’s just good.”

The couple’s son Dakota was both in April 2021. Culkin and Song got engaged less than a year later, and went on to welcome a second baby boy in March 2023.

Song and both boys were in attendance at Culkin’s Hollywood Walk of Fame star ceremony this past December, where he shouted them out during his emotional speech.

“You are absolutely everything. You’re my champion,” he told his fiancée directly from the podium.

“You’re the only person happier for me today than I am. You’re not only the best woman I’ve ever know, you’re the best person I’ve ever known.”

Macaulay Culkin and Brenda Song with son Dakota in Hollywood, California, on Dec. 1, 2023.AMY SUSSMAN/GETTY

While attending an event to celebrate the launch of Clarins’ new Multi-Active collection earlier this month, Song spoke to PEOPLE about when she feels the most beautiful — and “it has a lot to do with my partner,” she said.

“I think he’s the one that really made me feel the most beautiful when I’m about to go to bed and I have nothing on my face and I’m so tired,” the Social Network star explained of Culkin.

She added, “We’re about to watch some really silly thing on TV, and he looks at me, and [I’m like], ‘He makes me feel so confident.’ “

“I have someone who makes me feel beautiful without a stitch of makeup on, because he has to sit through my 20-minute self-care at night,” the actress said.