The popular Perth author announced the news in her typical candid manner, posting to Facebook she had 'no idea how it slipped through.'
The caption read: 'The commune is welcoming another baby. We tried everything, on and off bouts of the pill (until it flared my colitis too much). Withdrawal. Morning after pills. We actually have no idea how this baby slipped through. But it did.'
The author of Like A Queen became engaged to her current partner Denim Cooke in April after deciding to split with estranged husband Bill Mahon.
The post also said, 'We are our kids biggest fans and we don't see the harm in putting a new little soul right in the middle of it all.'
Hall already has four children with Mahon, making the new bub her fifth.
Cooke has two children from a previous relationship, bringing their total household number to six.
Hall’s fans flooded her post with more than 5000 comments and 70,000 likes, sharing pictures of their own blended families and sending well wishes.
The couple's new bub is expected in June 2018.
Congratulations to the growing family!