The couple have a 1-year-old son together and Ainsley is pregnant with their second child.
Ritchie also has two sons with his ex-wife, U.S. pop star Madonna.
"They're over the moon in love," an insider told People.com about Ritchie and Ainsley.
Ritchie's films include "Sherlock Holmes," "Snatch" and "Lock, Stock and Two Smoking Barrels."
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