Jana Duggar is speaking out as her brother Joseph Duggar's arrest sends shockwaves through the family and she says they never saw it coming.

The "Counting On" alum took to Instagram Thursday, insisting the Duggars had "no prior knowledge" of the allegations before they became public.

"We are deeply saddened and heartbroken," Jana wrote, describing the situation as shocking and painful for the entire family.

She didn't hold back on the seriousness of the accusations either, adding, "Our hearts are with the child who has been harmed -- this is a grievous and unacceptable wrong.”

As we reported ... Joseph was arrested amid allegations of abuse involving a girl who was 9 years old at the time of the alleged incident. He now faces multiple charges tied to alleged sexual misconduct with a minor and has pleaded not guilty. Joseph was released from a Florida jail after posting $600K bail.

Jana's sister Jill Duggar and her husband Derick Dillard previously said they were "shocked and heartbroken," condemning abuse and expressing support for the alleged victim.

Jim Bob and Michelle Duggar said they're focused on supporting the family, including Joseph's wife, Kendra, and their children ... while praying for the victim.

Kendra has also been arrested on unrelated charges, adding to the family's mounting legal issues.