Miss Ross insisted that Hudson join her during her show on Wednesday night, held at The Chicago Theatre in Chicago, IL -- which happens to be the "American Idol" star's hometown.
Hudson couldn't contain her shock and excitement, documenting the life changing moment from beginning to end.
"I did not see this coming ! On tonight I went to see @dianaross in concert , at best I wanted a picture," she wrote on Instagram. "So I surely didn’t expect or believe it when they told me @dianaross want you to come to the stage!"
Hudson's not lying -- she was seriously shook which is evident by this video.
"If @dianaross say for u to come to the stage , u come to the stage," she emphasized.
The duo belted out "Endless Love," the 1981 hit Ross originally sang with Lionel Richie.
Their performance happened after Ross put Hudson on blast in front of the crowd for not attending her star-studded 75th birthday back in March.
"You didn't come to my birthday, Beyoncé was there," she teased.
Indeed, Beyoncé was. In fact, Queen Bey even honored the legendary singer by being the person who sang "Happy Birthday" to Miss Ross.
Other stars in attendance for the mega-bash included Diddy, Khloé Kardashian, Kris Jenner, Heidi Klum -- the list goes on and on.
After Hudson joined Ross onstage and belted out some hits, she finally got her picture with icon.
Hudson was clearly beaming with happiness as Ross hugged her tightly backstage.
Let's not forget, Hudson starred in "Dreamgirls" alongside Beyoncé. The 2006 film was based off the Motown group "The Supremes" whose core was Ross, so she shouldn't be too surprised the legend wanted to hang with her.