"Look who's 4 months today! #BabyBeau #summerdays #summervibes #BeauBeauStyle #BeauIsMyBae," the former 90210 star captioned the photo which features Beau lying on his back with a shirt that reads, "Always on a vacay."
Spelling gave birth to her fifth child with her husband Dean McDermott in March. Beau weighed in at 5 lbs., 12 oz. and measured 18 and a half inches long.
"We are over the moon in love with baby Beau. He is a true blessing and his brothers and sisters were overjoyed to meet him! We are all truly grateful for our big beautiful and healthy family," the couple said in a statement at the time.
Spelling, 43, and McDermott, 50, are already parents to Finn, 4, Hattie, 5, Stella, 8 and Liam, 9. McDermott also has an 18-year-old son Jack from a previous marriage.
Spelling and McDermott last made headlines in May when a California judge directed the pair to pay off $220,000 in debt after they missed a court appearance. The judgement was part of case between the duo and City National Bank over accusations they have not paid off a $400,000 loan.