James told BBC Radio 2's Zoe Ball: "I must be able to tell you? Beyoncé. Beyoncé is performing tonight.
"She's performing a track she has never ever performed live before. Ever."
Queen Bey will reportedly perform five songs from her new album ahead of the first night of her Mrs. Carter Show World Tour in Glasgow on Thursday.
It will be her first appearance at the Brits in 10 years. She last performed in 2004 after she split with Destiny's Child, singing hit solo single 'Crazy In Love'.
A journalist for The Sun wrote on Twitter: "Beyoncé is currently at the O2 Arena for rehearsals. Organisers must be breathing a sigh of relief"
Beyoncé is currently at the o2 Arena for rehearsals. Organisers must be breathing a sigh of relief #BRITs2014— TomThorogood (@TomThorogood) February 19, 2014
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