The actress gave birth on Saturday.
The actress shared the first photo of her newborn son -- and revealed his name -- on Wednesday, four days after giving birth.
"Welcome to the world Vanja Sevigny Mačković Born May 2nd New York City," Sevigny captioned the pic, which shows her sweetly looking down at her baby while her boyfriend, Sinisa Mačković, stares into the camera, leaning his head on her shoulder.
"Thank you to all the staff at Mt. Sinai East for your bravery, perseverance and kindness, especially the nurses for being so gentle and patient. Blessings to all the other families giving birth during this time," she continued, adding the hashtag, "#ilovemyboys ?."
Sevigny revealed in a recent Q&A for Homme Girls that she and Mačković were having trouble deciding on a name for their little one.
"Our baby's due in 8 days and we don't have a name yet," Sevigny said at the time.
TMZ was first to report in January that Sevigny was pregnant and that she's been dating Mačković, who is the director of Karma art gallery in New York City, for more than a year. The 45-year-old actress had since documented her pregnancy on social media.
See more on Sevigny in the video below.