The 28-year-old rapper was "blown away" when she saw YouTube footage of internet sensation Sophia Grace and her five-year-old cousin Rosie perform her track 'Super Bass', and surprised the English children when she arrived on the programme to join them in a rendition of the song.
Nicki told Ellen: "She blew me away. Within five seconds of seeing her video, I was calling everyone! I was also receiving a billion emails. Everyone was like, 'you have to see this little girl.'"
Rosie doesn't sing in the video, but dances along as Sophia sings and Nicki said she enjoyed their pairing.
She said: "I have a hype man, and you have a hype girl."
Before singing with the youngsters, Nicki praised Sophia's talent, but urged her to put her education first before embarking on a singing career.
She said: "Seriously, we are watching a Journey that's about to be amazing.
"You are incredible. I just want you to stay in school. Music is beautiful, but stay in school, OK? Put your books first and singing second."