'Home Alone' Star Macaulay Culkin Reacts To Catherine O'Hara Death

Macaulay Culkin is reacting to the sudden death of his "Home Alone" costar Catherine O'Hara ... and he's lamenting the fact he won't see her again in this life.

The "Home Alone" star took to Instagram on Friday to share a tribute to Catherine, who played his mom in the two original Christmas classics.

Macaulay shared a photo of him and Catherine from the end of the OG "Home Alone" and another shot of them later in life, from the same angle as the movie still.

He writes ... "Mama. I thought we had time. I wanted more. I wanted to sit in a chair next to you. I heard you. But I had so much more to say. I love you. I’ll see you later."

TMZ broke the story ... Catherine died Friday in Los Angeles. She was 71.

The official cause of death is unclear, but we know Catherine suffered a medical emergency at home and was rushed to a hospital hours before she died.