Fergie and her husband Josh Duhamel went to watch Britney Spears at her Las Vegas residency and was thrilled by her performance, writing on Twitter "#youdrivemecrazy (sic)".
The 38-year-old singer and her hunky actor husband went to see the 'Perfume' hitmaker at one of her shows at the Planet Hollywood Resort and Casino earlier this week, where they were joined by model Daniel Garofali, William Derella and Sean Patterson.
Fergie wrote on Twitter: "Ms Brit #youdrivemecrazy (sic)"
The Black Eyed Peas star also attached an image of the Britney who was on stage, wearing a black mesh leotard accesorised with sequins, with her hands on her hips while she was surrounded by dancers.
Fergie later added: "About last night... #britneyshow #workbitch (sic)", with a picture of her and her pals posing for the shot.
She's not been the only star to go and see Britney's 'Piece of Me' show.
Nicole Richie was "crawling on all fours" at the show on Tuesday night (18.02.14) and the pop star later thanked the 32-year-old beauty.
Britney wrote: "Can we all give a round of applause to @NicoleRichie for playing along in the show tonight? U looked hot crawling on all fours ;). (sic)"