The veteran star took to her Twitter.com page on Thursday (18Jul13) to announce the happy news she is the grandma to a little girl named Rio, who she notes is the first female grandchild to join the family.
She writes, "Welcome Rio! Our first baby girl to join our family! (Oliver Hudson) and Erinn thank you for bringing so much Joy to our lives! happiness"
The Rules Of Engagement star and Bartlett already have two sons, Wilder, five, and three-year-old Bodhi, while his actress sister Kate Hudson has two sons - Ryder, nine and Bingham, two.
Further details about the birth have yet to be announced.