Duchess of Cambridge's sister Pippa Middleton, whose derriere has been as talked about as that of American reality TV star Kim Kardashian, says their shapely curves are not at all comparable.

Middleton has written an article for the August political weekly, The Spectator, in which she has drawn a comparison between her derriere with that of Kim, who recently posed naked for a magazine, reports dailymail.co.uk.

"The 'Rear of 2014' award undoubtedly goes to Kim Kardashian, after her posterior exploded all over the internet last month," wrote Middleton, whose own backside was considered to be the 'Rear of 2011' when she wore a tight-fitting bridesmaid's dress to the Royal Wedding.

"I must say that mine -- though it has enjoyed fleeting fame -- is not comparable. But the Kim bu** story did make me pause. What is it with this American b**ty culture? It seems to me to be a form of obsession," she added.