"She has inspired dancers and choreographers all over the world," Hough shared, before explaining that Davis was "unfortunately was diagnosed with seven auto-immune diseases that left her terminally ill."
Davis channeled her tragic diagnosis and the medical obstacles she's facing into her choreography, and cast Hough to embody her spirit in the routine.
"This dance is Marinda's story that she's choreographed. I could not be more honored that she chose me to play her, and that we get to share her gift with the world," Hough shared.
The deeply emotional number was set to "Wouldn't Change Anything" by the band Alexander Jean -- made up of DWTS pro Mark Ballas and wife BC Jean -- and told a heartbreaking story of Davis' emotional journey.
The striking performance -- set in an ambiguous time period in the past -- began with Hough stepping out of the door to a doctor's office, looking scared and stunned, and followed her as she performed with a group of dancers around a town square.
After some breathtaking choreography, Hough fell to the floor motionless, surrounded by the other dancers who mourned as the dancer was lifted up into the air by cables, symbolizing her death.
Davis was in the DWTS audience and spoke with host Tom Bergeron after the powerful performance.
"I have to say how much I admire you turning what you're facing into art," Bergeron marveled.
Davis, who said the experience was "a dream come true," expressed effusive praise for Hough's skillful display, sharing, "She's so incredible. As you guys just saw, she's a wonderful performer, but what people may not know is she's one of the most extraordinary humans I've ever worked with and known. I just adore her."
Hough spoke with ET's Cameron Mathison backstage after the show, and gushed that it was "amazing" to be back in the DWTS ballroom.
"I obviously have been watching this season while shooting in Alabama," she said. "I've kept up with it... When they asked me to come back on as a guest judge, I was like, 'Absolutely, on one condition!' and that's how I got [to do] the performance for my friend Marinda, who has obviously been battling a lot of things."
So will she be returning to DWTS anytime soon?
"To be honest, I'm not sure," Hough admitted. "I'm focusing more on my acting and I'm so excited we just sold a show to Fox that I'm producing and starring in."
However, the triple threat didn't hesitate to add, "This is my home, this is where it all started. I'll never be away from Dancing with the Stars!"