Rory Culkin says "everything has become a little heavier" since he became a dad.

The 36-year-old actor and his girlfriend, cinematographer Kate Arizmendi, welcomed a baby girl named Havoc Moon into the world on May 24.

And in one of his first interviews since becoming a first-time parent, Rory - the brother of Macaulay and Kieran - reflected on how baby Havoc has changed his life.

He said: "Having a child introduces you to time, and now everything just feels a little heavier. I mean, when I have to say goodbye to her, I get choked up on the train.

"There's just more gravity now, you know?"

Rory, who made his acting debut in 1994 movie Richie Rich, playing a younger version of older brother Macaulay's character, added to People that fatherhood has been "lovely" so far.

He gushed: "Really such a pleasure. Everyone was telling me how difficult it is, and it is, but that's outweighed so much by the love."

Meanwhile, Rory told Entertainment Tonight that welcoming baby Havoc into the world has also meant that he has regained something of a "throne" in his family.

He laughed: "I was always kind of mad because I've always been the youngest Culkin -- until they started having kids.

"But now I have the youngest Culkin, so I reclaim the throne!"

Kieran has three kids with wife Jazz Charton - Kinsey, Wilder and a third baby, whose name and gender is unknown - while Macaulay has two sons with fiancée Brenda Song, Dakota and Carson.

Kate announced news of Havoc's birth in a post on her Instagram Stories, posting an adorable shot of their bundle of joy sleeping with the caption: "Her in the womb while I'm screaming System of a Down. We're so in love with you."

In a second story, Kate uploaded a photo of her and Rory's daughter looking wide-eyed down the camera, with the caption: "15 mins after pushing her out and so alert and excited about life already. "Also hello girl baby Rory."

And in a third story, Kate posted a shot of Rory cradling Havoc whilst sitting in a chair, with the caption: "Best papa."