The US superstar is one of several acts - along with Bon Jovi, James Blunt and Eliza Doolittle - set to play at the royal couple's Winter Whites Gala in London's Royal Albert Hall on December 8, in aid of homeless charity Centrepoint, and she is thrilled to have been asked.
In an interview with UK station BBC Radio 2, she said: "I'm really excited, I'm going to be playing the Winter Whites Gala, I'm really stoked, it's the first royal engagement I've done and I feel very honoured."
And the 'I Knew You Were Trouble' hitmaker is already thinking about what to say and do if she gets the opportunity to meet the royal couple at the event, but she isn't getting her hopes up.
She said: "I've been asking about that [etiquette], I think I'm safe if I just shake hands and be polite. I think it's presumptuous to assume I'll meet them, so first I'm going to be polite enough to not assume I'll meet them."
The blonde beauty, 23, will then return to London with her 'Red' tour in February 2014 and was astonished by how popular her concert dates have proven.
She said: "I'm doing five shows at the O2 [in London] which I'm beyond thrilled about, I'm beyond honoured that the fans sold out five shows, that was beyond my expectations."
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