The singer attended the rapper and his gal's nuptials at Babington House in Frome, Somerset, with her hubby Sam Cooper.
She wore a gorgeous vintage-looking monochrome maxi dress with a check board top and a keyhole cutout at the bust.
She paired her dress with towering black platforms, a black Chanel handbag, and a pair of Ray Bans.
Lily was, however, spotted not-so-stylishly sneaking off for a cheeky ciggie before the ceremony. Slapped wrists, Lil.
Lily has a love of fashion, famously opening a vintage clothes store, Lucy In Disguise, on a TV documentary called Riches To Rags.
Wonder if she dipped into the collection for Millie's wedding? See pics of the nuptials here, and check out more Lily fashion moments below: