Evan Agostini / Invision/AP 1 / 15
Evan Agostini / Invision/AP 1 / 15

See Sienna's bump!

Sienna Miller hasn't spoken much about her first pregnancy -- but she didn't need to say a word at Tuesday night's opening reception for W magazine's "Ever Changing Face of Beauty" exhibit at the Park Avenue Armory in New York.

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Clad in a tight black halter dress, the British actress, 30, debuted an undeniable baby bump. The low-key star has been similarly mum about her engagement to the baby's father, fellow British actor Tom Sturridge. She flashed a giant diamond and platinum engagement ring while out and about in London last Friday.

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"Friends are really happy with her relationship with Tom," a source told Us Weekly back in January of Sturridge, 26, her beau of over a year. "He's younger, yes, but he's mature and he's a good guy."

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Miller and Sturridge's friends "were not surprised by the news of the pregnancy," says the source. "They're really good together."