"I was really excited," Derick Dillard told PEOPLE. "As a new dad, to have a firstborn son to be our first child and be the leader of his siblings, it is very special."
Before her ultrasound appointment last Saturday, Jill indulged in a sugary breakfast of waffles with syrup and whipped cream, fruit, chocolate milk, and lemonade. She wanted to make sure Baby Dilly would be active for his big debut.
"He stretched out his legs full length," said Jill. "He was trying to be like Dad."
Jill and Derick brought three Duggars--Joy-Anna, James, and Jennifer--with them to the appointment. Jill said there was "screaming in the room" when the gender was revealed.
Jill had predicted that Baby Dilly would be a girl, but both she and Derick agreed that, boy or girl, all they wanted was a healthy baby.
Both the Duggars and Dillards were thrilled to hear the news.
"We could have a giant," said Jill. "I called Derick's mom, and she was telling me that when Derick was born, he didn't fit into the newborn clothes, and his shoes were a size two."
According to Jill, her parents were "just elated."
"My mom and dad both thought it was going to be a boy and my grandma did, too," said the expectant mother. "They are all really excited,"
Jill and Derick don't plan on following a letter theme for their children's names, but they might choose a different theme, such as family names.