Nicki was 'blown away' when she saw YouTube footage of Sophia Grace, eight, and her five-year-old cousin Rosie perform her tune Super Bass, and surprised the British kids when she appeared on the US show by joining them in a rendition of the song.
The 28-year-old told host 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.
Before singing with the pair, Minaj praised Sophia's talent, but urged her to put her education before her singing career.
She said: 'Seriously, we are watching a journey that is 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 your singing second.'
The youngsters achieved instant fame when their rendition of Nicki's hit Super Bass went viral, achieving around 8 million views on YouTube so far.