"I was not thinking that God would give us another one, and we are just so grateful," Duggar, 45, told NBC News Friday.
Father James Robert -- or Jim Bob -- said their children, who span from 23 years to 23 months old and all bear names beginning with the letter "J," thought he was joking when he informed them, "Smile -- Mom's going to have another baby!"
"Their mouths dropped," Michelle laughingly said. "They all looked at me to see if he was joking."
The Duggars, who live in Tontitown, have their own reality television show on The Learning Channel, "19 Kids and Counting."
Jim Bob and Michelle Duggar eschew birth control and say they leave family planning up to God, NBC reported.