The couple revealed the heartbreaking news via Lisa's Raddest Mom blog on Friday morning (6 September) in a post titled 'Unfortunate Announcement.'
Lisa wrote: "I have been dreading this announcement…. I needed some time before being able to say it. Jack and I lost our baby boy last week."
"Having a late term miscarriage is by far the hardest thing either of us have ever had to go through. We appreciate all of your prayers and ask for privacy and respect during this time."
She added: "It's important to stay hopeful and optimistic through life's toughest moments. We never know why things like this happen. All we can do is trust in God and know he has a plan for our lives."
Cuddling my amazing, sweet hubby & shutting my eyes. Thank you all for the love & support. It means the world.— Lisa Osbourne (@MrsLisaOsbourne) September 6, 2013
Lisa later posted a brief Twitter message thanking fans for their messages of support.
"Cuddling my amazing, sweet hubby & shutting my eyes. Thank you all for the love & support. It means the world."
Jack and Lisa are parents to one-year-old daughter Pearl.