The Olympian and former I'm A Celebrity star highlighted her blossoming tummy in a beautiful fitted pale pink dress that fell just above the knee.
And just in case we missed the bump, she drew attention to it by placing her hand across her midriff while on the red carpet!
Rebecca, 25, announced her first pregnancy this month.
She married fellow swimmer Harry Needs in August, following a March 2013 engagement. They've been together since 2011.
Their baby was conceived on honeymoon in Venice – much to the surprise of Rebecca and Harry who didn't expect it to happen so quickly!
Rebecca told Daily Mail: "Harry and I thought that any time after we were married would be fine to start a family, but we didn't expect it to happen quite so quickly!
She added: "We both wanted to be married before we had kids. Even though we're not religious, we both come from traditional backgrounds and wanted to do it that way round.
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