Knoxville Mayor Madeline Rogero was with the producers for the big moment.
"I was able to be a fly on the wall to watch the process, and the family was overcome with emotion," Rogero said.
While the Watsons were learning the news, hundreds of volunteers were standing by ready to work and heavy equipment blocked the streets around Robinson Road.
The build is a huge project to pull off, from logistics to the design team.
Designer Tracy Hutson has been with the show all nine seasons. She says it never gets old, and the emotion you see on the faces of their team and the volunteers is real.
"We get very little preliminary design. Now that we've met the family, getting their favorite colors likes and dislikes and figuring out what furniture they want to keep and what to design in the house, it's go time," Hutson said.
"This is my favorite part. I mean this and when we move the bus when they come home," Hutson said. "Just seeing their video and seeing how passionate they are about helping other families just means the world to be part of it," she added.