Credit: Splash News Online

Baby and bling on board!

Now that Sienna Miller and her boyfriend of a year Tom Sturridge are expecting a baby, it appears that they decided to make their little family official!

On Friday in the hip Soho district of London, Miller, 30, was spotted with a giant platinum engagement ring on her finger. She complemented her dazzling new accessory with an edgy black manicure.

But fans can expect Miller to follow in the footsteps of other expectant stars like Jessica Simpson and Kristin Cavallari -- first comes baby, then comes marriage!

A source told Us Weekly in January  (before Sturridge put a ring on it) that the New Year's Eve actress and Sturridge, 26, "don't have plans right away to marry -- if at all."