Dimitrios Kambouris/WireImage; Barry King/Getty Macaulay Culkin (L); Brenda Song
The couple of four years (and new parents to 9-month-old son Dakota) are engaged, a source tells PEOPLE.
Song, 33, was recently photographed sporting a sparkling ring on her left hand while out in Beverly Hills.
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Culkin, 41, and Song met on the set of Changeland in Thailand and were first romantically linked when they were spotted out in July 2017.
The couple welcomed their first child, son Dakota, in April of last year. They named their son after Culkin's late sister Dakota.
"We're overjoyed," Culkin and Song said in a brief statement about the arrival of their first child.
The couple keeps their relationship private on social media although Song shared a special Instagram message to Culkin in August 2020 on his 40th birthday.
"Happy 40th birthday to this magical being," she wrote in the caption. "I could sit here and write endlessly about how wonderful, kind, loving, genuine, loyal, honest, brilliant and hilarious you are, and how grateful I am that I get to share and do this life thing with you."
The marriage will be the first for Song, while Culkin was married to Rachel Miner from 1998 to 2002.