Chip and Joanna Gaines on What Life Lessons Son Crew has Taught Them and Renovating a Castle (Exclusive)

The 'Fixer Upper' hosts sat down with ET and opened up about their personal lives and their exciting new series.

Between fixing up historic properties, starring in a hit home renovation series and parenting five children, it seems that Chip and Joanna Gaines have their hands full. However, that doesn't mean they aren't interested in possibly expanding their family sometime in the future.

The couple recently sat down with ET's Kevin Frazier, and they reflected on their adorable kids, and why Joanna still thinks about wanting more.

"I am terrified of that moment when our last one leaves," she said with a laugh. "For me, it's like if we can just keep having babies, then at some point it’s for sure I won't have to experience that."

Chip and Joanna share five children -- Drake, 17, Ella, 16, Duke, 14, Emmie, 12, and Crew, 4, however, as Joanna explained, "I think the more the merrier."

Looking back at their decision to have Crew eight years after welcoming their daughter Emmie, Chip explained that their youngest son gave them an opportunity to slow down a bit and enjoy life at a slower pace.

"I mean, we've always been busy. But then, we were busy trying to build a business and then we had four kids on top of that... I mean our lives were very chaotic," he shared. "Then we had about eight years where we thought we were done with new babies and we were raising the four that we had."

"Crew, really, just something about him was almost like a parachute at the end of a race car. It didn't force us to slam on the breaks, in the negative sense, it allowed us to really stop," Chip continued. "So for Jo and I, it's been this beautiful season where we've got these four older kids who treat this little boy [great] -- the way they love on him [and] tend to him in sweet ways."

"What crew has brought to me is just the idea of stopping and seeing the moments around me that are full of wonder," Joanna shared. "Whether it’s as simple a flower that’s growing in the grass. The crew has really done something to me where I’m typically, 'Go, go, go!' I have just wanted to step back and say, 'I’m gonna look for these moments of wonder.' Because that’s what my 4-year-old toddler has taught me"

"Crew has been a gift in so many ways," she added."

While the pair may not be contemplating a family renovation any time soon, they have been working on renovating a historic castle property in Waco, Texas, which they documented for their upcoming series, Fixer Upper: The Castle.

"For the last 20 years he's been trying to buy the castle," Joanna said of Chip's longstanding interest in the property. "It's gone on the market maybe four or five times in the last 20 years, and he got to the point where he wouldn't tell me anymore when he was putting an offer in!"

"The irony is that the only time that I could have actually afforded it was the time that it was accepted," Chip shared. "The other three opportunities probably would’ve bankrupted us! And I mean that literally. We would have immediately sunk the entire ship."

The Cottonland Castle was built in 1890 and took 23 years to complete. As one can imagine, restoring the historic, sprawling 6,700-square-foot home without losing or hurting its unique character was something of a challenge for the pair.

"This was our longest project by a long shot. Jo and I are wildly efficient we're typically on really tight budgets, tight timelines, this house would not allow for that. It wouldn't allow for the budget that we created for it," Chip recalled. "This thing took on a life of its own. It took longer, it took more money."

"I would say that's partly why we're so proud of it now that its in the rearview mirror," he added. "But during the project, it was exhausting and tiring and complicated."

According to Joanna, the entire undertaking took three years in total.

"We bought it, we planned a year of design, research, figuring out where we needed to get the materials, and then once we finally pushed go it was almost a year of construction," she explained.

As for what was the hardest part of the renovation, Chip said the biggest challenge came with redoing the outside of the massive property.

"For me, it's just the exterior stuff. Like the stone was the scariest decision for me, because if you mess that stone up, you know, it's like a facelift gone wrong, you know?" he explained.

"More than it being on Fixer Upper, more than anything, we wanted the neighbors to be proud of what we did with this thing," Joanna added. "It turned out great and were proud of it."

Fixer Upper: The Castle drops concurrently on Magnolia Network, HBO Max and Discovery+ on Oct. 14.