Britney is no stranger to showing off her hard work on Instagram of late, so when she posted a poolside bikini pic of herself with an incredibly slender stomach, no one really batted an eyelid - until someone noticed something going on around the small of her back... They're mostly wondering where the concrete's gone. 

One follower wrote: "It's been Photoshopped under her back. Where's the pool's edge? Clearly a photoshopped back arch”, and: "hahHahAhhHHhaA she has a hole in her back obv photoshop."

Others leapt to the singer's defence (sort of), saying: "You all are so irritating. Shes old enough to be most of your mothers and still crazy hot. Stop hating", while another added this theory: "Doesn't look photoshopped to me. The "blue" water you're seeing under her back is her shadow. The shadow is casting the entire area beneath her (sun seems to be beaming directly on top of her). The grass beside her appears to be lumpy due to perhaps, bad landscaping or well, nature being nature. Plus, the grass in the background has similar features. I don't think this is photoshopped. If so, oh well. Let's all carry on."