The new addition was welcomed by his parents, Dunst, 35, and Plemons, 30, over the weekend.
Multiple sources told WHO's sister publication that the proud parents of the “healthy baby boy" are "doing great!"
Representatives for the pair are yet to have to comment on the exciting baby news.
The arrival of their newborn comes four months after Dunst confirmed her pregnancy in January in the Fall/Winter portrait series for Rodarte — a fashion label co-founded by her dear friends, designers Laura and Kate Mulleavy.
Stay tuned for pictures of the new bub!