Rebecca beamed from ear to ear as she walked the red carpet at The Sun Military Awards in an electric blue gown.
The dress, which was ruched at the waist, accentuated Rebecca's baby bump.
The Olympic swimmer also flashed some leg thanks to the gown's thigh high split, and her wavy locks draped over her shoulders to create a perfect red carpet picture.
The annual awards ceremony, which honours members of the British armed forces and civilians involved with the forces, was held at the National Maritime Museum.
Taking to Instagram, Rebecca said: "Amazing night at The Sun Military Awards. Incredible honour to be in the same room. What they all do is just unbelievable #military #heroes."
It turns out Rebecca did a bit of celeb spotting too, as she grabbed a photo with Simon Cowell and David Beckham!
While Rebecca called Simon a "lovely man", she gushed about David: "Couldn't of been more starstuck! I was like a little kid in a sweet shop!"
Just over a week ago, former I'm A Celebrity... Get Me Out Of Here! star Rebecca told fans she was expecting her first child with husband Harry Needs.
Commenting on the news over Twitter, Rebecca revealed: "Thank you so much for all the lovely messages!!! Really kind. We're so excited! I can't wait to be a mum!"
Rebecca, who is expected to give birth in June next year, is planning on a water birth.
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