The midi-length strapless ivory tulle number she sported to wed James Righton in France in May was from Chanel's spring/summer 2006 haute couture collection. She had first worn the gown to a Bafta after party in 2008.
The dress got its third thrifty airing last night, but the actress added a chic twist to make it a little more winter appropriate.
Attending the SeriousFun Children's Network London Gala, with her husband on her arm, Knightley wore a sheer, long-sleeved embellished top - not by Chanel - underneath the dress.
While a three-times worn Chanel couture dress is hardly thriftiness personified (it will likely have cost upwards of £10,000, though we're sure Keira, a Chanel ambassadress was gifted it) it's nice to see that Knightley's not afraid to let her pricey pieces work hard for her, rather than hide them away in a wardrobe.