Congratulations to Kate Winslet and Ned Rocknroll -- the happy couple just welcomed their first son together on Saturday, Dec. 7.

"Mother and baby are doing great," Winslet's rep told PEOPLE.

The little boy, who was born in Sussex County, England, arrived into the world weighing 9 pounds, the Daily Mail UK reports. According to the newspaper, Winslet's spokesperson referred to him as "Baby Boy Winslet." (No Baby Rocknroll?)

Winslet and Rocknroll (the nephew of billionaire Richard Branson) tied the knot last December and revealed that they were expecting in June. This is the third child for the Academy Award-winning actress, who is already "mum" to 13-year-old Mia (with ex-husband Jim Treapleton) and 10-year-old Joe (with ex-husband Sam Mendes.)

Both Winslet and Rocknroll couldn't wait to become parents together, and are "thrilled to bits" at the birth of their son, Winslet's rep told the Daily Mail.

Congratulations to the happy couple!