Sienna and Tom - best pals with Robert Pattinson - have been dating for over a year, and Sienna showed off an engagement ring back in February.
The actress showed off her baby bump style back in May when she attended R-Patz's 26th birthday at Claridge's in London in a stretchy grey jumper dress and black blazer.
Congratulations to the new parents, and watch this space for all the details.
See more baby bump style below:
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