Sienna Miller Credit: Splash News Online

Sienna Miller didn't let any pregnancy pains prevent her from celebrating her fiance's BFF's 26th birthday.

So in London on Sunday, the pregnant actress, who is expecting her first child with fiance Tom Sturridge, made her way to Robert Pattinson's birthday dinner at Gordon Ramsey's restaurant in the Claridges Hotel. Sturridge, an actor himself, and the Twilight star are good friends.

For her night out, she showed off her growing baby bump in a short gray jersey mini accented with a striped belt that hugged her belly, gold peep-toe booties and a black sweater.

Earlier this month, Miller, 30, and Sturridge, 26, jaunted off to Portofino, Italy for a babymoon -- a romantic trip that couples sometimes take to enjoy quality time together before baby-to-be arrives.

With her platinum diamond engagement ring on full display, the actress, whose hair appeared to be a couple of shades darker than her normal sunny blonde hue, was all smiles during their outings.

In January, Us Weekly broke the news that Miller, whose famous ex is Jude Law, and Sturridge were expecting their first child together after being together for a year. A month later, she was spotted with a diamond engagement ring.

Finally, in March, the star, who had kept mum on her engagement and pregnancy, opened up about her pregnancy to British Vogue, calling her mommy-to-be status "very exciting."