Tulloch, 35, and Giuntoli, 36, decided to share the news as they found the event appropriate, reported Entertainment Weekly.
"We did decide that Comic-Con... I was going to wear the ring out in public for the first time," Tulloch said.
Meanwhile Giuntoli was unable to hide his happiness and confessed, "We've just been quietly enjoying it."
Earlier the American-born actress clarified, "It's pretty public now that I'm dating David, so that's kind of out of the bag. We were hiding it for a long time, but now everybody knows."