"He said I'm the biggest thing in Ireland," she said while clutching the note. "Bitch this is f-cking Bono. He knows me. He f-cking knows me, bitch. I can't believe it. I can't motherf-cking believe it. Nobody talk to me now."
Although the letter was hardly legible, the legendary performer's signature is clear on the paper.
Waiting for your permission to load the Instagram Media.
Cardi B later thanked Bruno Mars on Instagram for the opportunity to perform their hit "Finesse" on the Grammy stage.
"I want to thank you so much. I don't even know how," she wrote. "Maybe one day you'll need a kidney. I got you. Congrats on your wins tonight. You deserve it. You sing, dance, play instruments, produce your videos SHIT you probably know how to build a house, You ARE AMAZING and you gave me rhythm."