In this week's issue of People magazine, the 43-year-old revealed she was taken by "surprise" as she opened up about the prospect of becoming a mother again.
"It was a total surprise," she confessed. "But we always wanted a big family. I’m really excited."
Tori Spelling is expecting her fifth child with her husband Dean McDermott
"Dean was saying, 'We just got Finn out of diapers; I thought we were in the clear!'" she added. "For the first time this year, they’re all in school. So it’s like, wow. We’re basically starting over."
The couple, who celebrated their tenth wedding anniversary in May, are parents to four children - Finn, four, Hattie, five, Stella, eight, and Liam, nine.
Dean, 49, also has an 18-year-old son, Jack, from his first marriage to Mary Jo Eustace.
"This baby happened at the best time," the actress continued. "Nothing is ever perfect, but I’m so madly in love with my husband and with our kids. The idea of adding to that is such a blessing."
The couple are already parents to four children - Finn, four, Hattie, five, Stella, eight, and Liam, nine
This news comes four years after Tori nearly died in childbirth, following complications during her pregnancy with Finn.
In 2013, problems in her marriage surfaced when it was revealed Dean had been unfaithful - which was well documented in their reality show True Tori.
"As all of you know, our family has been through a lot this last year," the TV star wrote in her blog shortly after the revelation. "I'm happy and proud to say that we are doing really well, and that Dean and I are working very hard to make our relationship and our family better than ever.
"I'm proud of Dean for all of the hard work he's been doing on himself," she added.