The couple confirmed the joyful news on Thursday (02Mar17), in a statement to People magazine.
"We are over the moon in love with baby Beau," Spelling gushed. "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."
Spelling also shared the announcement on Twitter.
"We are so excited to announce the birth of the newest member of the MCDermott family! Please join us in welcoming Beau Dean McDermott," the former 90210 star wrote.
The 43-year-old and MCDermott revealed they were expecting a new addition to their family last October (16).
Beau Dean joins four siblings, Finn, four, Hattie, five, Stella, eight and nine-year-old Liam. Actor MCDermott also has an 18-year-old son, Jack, from his marriage to Mary Jo Eustace.
Tori didn't anticipate having a fifth child after suffering from placenta previa, a serious condition in which the placenta blocks the cervix, during her pregnancy with son Finn.
"I thought if we had another baby, my life could potentially be in danger," she told People magazine last year. "Dean and I created four beautiful children together and the thought of them not having a mother (if something went wrong again) was not something we were OK with."
But the star was given the all-clear this time around.
Tori and Dean, who have appeared in a series of reality shows, wed in 2006 but their marriage was rocked in 2013 when Dean was accused of cheating on her. After working on their marriage, Dean pledged his love to Tori once again by proposing to her in Paris in April (16) surrounded by their children.