However, whilst we were busy nodding in approval of another style success from Sam Cam, we failed to notice that Carey Mulligan had already worn the dress to the American Film Institute's Young Hollywood's Roundtable event in LA last year.
Mulligan teamed Pilotto's s/s 2011 design with a pair of peep-toe pumps and a scraped back updo, while Cameron opted for a more sensible pair of grey stilettos. Her hair and makeup was simple and chic as usual.
It's a tough call, but who looks the best? The young starlet or the PM's wife? Let us know by voting below.