Speaking at the Glasgow auditions earlier today (12th June), Digital Spy quotes Walsh as saying: "I loved Britney. She is such a star. She's really bright, really brilliant, she has it totally sussed."
The 59-year old was previously teased by Spears and fellow XF USA judge Demi Lovato before taking Cowell's seat, with Lovato calling him a "substitute teacher" on Twitter.
Britney later pretended that she didn't know who Walsh was, tweeting: "Louis? That guy is on the real housewives or something... right? (sic)"
The pop princess then stated: "Just kidding! Love Louis. Met him at @TheXFactor in the UK! Welcome to the @TheXFactorUSA gang."
Despite welcoming Walsh, Spears went on to add that she was missing Simon, writing on Twitter: "I can't believe I'm actually saying this... but I miss @SimonCowell. Hope you feel better soon!"