Katy Perry threw on a Yankees hat ... and belted out a rendition of the Jay Z/Kanye West track, "N**gas in Paris" ... and it's ... interesting.
It all went down a few hours ago during a performance for BBC Radio 1 in London. Don't worry, Katy used the word "ninjas" instead of the OTHER n-word.
It ain't the first time Katy's covered a Jay Z rap song ... last year she covered "Big Pimpin'" during a performance in Auckland.
But back to the new song ... we gotta ask ...