Song met Culkin in 2017, while they were both filming the movie Changeland. For the first few years of their relationship, she didn't comment much on it publicly, although she did tell Us Weekly in 2018, "I don't like to talk about my personal life, but everything's wonderful and I'm happy."
In 2020, the couple spoke to Esquire for a cover story. "People don't realize how incredibly kind and loyal and sweet and smart he is," said Song, as People reported. "Truly what makes Mack so special is that he is so unapologetically Mack . . . He knows who he is, and he's 100 percent okay with that. And that to me is an incredibly sexy quality."
The couple also shared that they were trying for a baby in the same interview, and they didn't have long to wait! In April 2021, they announced that they were now parents to a son, Dakota Song Culkin.