The 39-year-old actress stepped out with the new accessory on November 2 - with many think Foxx had gone on bended knee.
Holmes' rep quickly quashed all chatter of marriage, telling PEOPLE that it is not a real engagement ring.
“Katie’s not engaged to anyone besides her fictional movie fiancé, played by Jerry O’Connell,” her rep explained.
An insider told PEOPLE, “Everyone knows they are dating, but they still want to keep it private.
“After the beach pictures, they only spent time together at home and got extra careful. But this year, they have been more social together. They often go to restaurants for dinner dates, or to hang out with friends.”