The couple have kept their baby news away from the public eye until now and still haven't commented on the pregnancy.
But it was very clear after the 33-year-old actress was pictured wearing a fitted black maxi dress which drew eyes to her blossoming bump.
This will be Riley's first child.
Hardy married Riley in July 2014. He is already dad to son Louis, who was born in 2008 from his relationship with Rachel Speed.
The 37-year-old actor has previously spoken out about how fatherhood has "saved" him from his drink and drugs addiction.
He told the Metro: "I had no idea how to handle the industry, to interact with producers, executive producers, studios… I was 24.
"It’s taken being someone’s dad, being divorced, going to rehab, having mortgages, playing different characters, doing theatre, waiting and then it not happening.
"And then doing rather well at something, enjoying my character work, but it not being a huge amount of money."