Macaulay Culkin has penned a heartfelt birthday message to his fiancé, Brenda Song.

The Home Alone star expressed his deep affection for the Secret Obsession starlet referring to her as "my best friend" in the heartwarming note.

Taking to his Instagram on Wednesday, Culkin dropped two snaps, the first image showcased Song donning a white bathrobe with a towel draped around her hair.

He also added a snap of the top portion of a milk carton, which displayed a sell-by date of 3/27/2024.

Culkin wrote, in the caption, “Happy birthday to the best friend, mother, ally, colleague, lover, and partner I could ever wish for. You are my reason. I love you.”

The Good Son also quipped in his post referring to the milk carton, “P. S. The milk is due. Can you pick some up on your way home from work?”

Read also: Macaulay Culkin receives emotional Walk of Fame Star, joined by 'Home Alone' mom

Soon after, he posted a wish for his fiance, the fans flocked to the comment section to gush over their bond.

One fan wrote, “Happy Birthday to the woman who brought back the light and saved our Beloved Kevin McCallister. Thank you for being a Hero, we love you Brenda”

Another noted, “The absolute best. Sometimes I think about y’all together and cry from too much joy. You both deserve the very best. Happy birthday to your love!!!”