Sienna Miller in BOSS Black | “The Ever Changing Face Of Beauty” Reception

Sienna Miller finally debuted her new pregnancy figure on Tuesday night when she attended The Ever Changing Face of Beauty video installation by Solve Sundsbo opening reception hosted by Stefano Tonchi, Editor in Chief of W Magazine.

The 30-year-old English actress wore a black halterneck floor-length dress by BOSS Black with front and side slits in the skirt as well as the center neckline. This design was perfectly form-fitting and looked amazing on her; the high slits also gave a great view of Sienna’s platform blue sandals.

She completed her look with a metallic bronze clutch that matched her edgy jewelry by Pamela Love. Sienna wore her long blonde locks up in a high-volume style and rocked a cool cat-eye.

Sienna is expecting her first child with fiancé Tom Sturridge this spring!