"Brooksie told me 'I got this' Sooo Proud of his new baby Grey 'Jack and the Beanstalk Batman' #finallyhere #firstvisit," she wrote alongside another sweet pic of Brooks holding his little brother, referencing the name her son picked out for the new addition.
Sims announced on Wednesday that she and husband Scott Stuber had welcomed their third child.
"???Welcome to the world Grey Douglas Stuber 1.10.17 Words do not express how grateful and happy we are to have another piece of magic added to our little tribe! #blessed ?#tribeof5," she captioned the adorable announcement photo.