Carlyle told TV Line that the spell - which traps fairytale creatures in the real world town of Storybrooke - may have surprising origins.
Carlyle also revealed that the relationship between Gold and Regina (Lana Parrilla) could be changed as a result.
"Certain things happen toward the last five or six episodes that shake our relationship," he teased.
"You realise that maybe Rumpelstiltskin [didn't create the curse] for her at all - maybe he was doing it for himself. Maybe the curse was created for him."
Once Upon A Time star Ginnifer Goodwin recently revealed that she knows what breaks the curse, adding that when she found out she "felt like a dumb-dumb because it makes perfect sense".
Meanwhile, the show's producers have revealed that fans will find out more about Rumpelstiltskin in future episodes.
Once Upon A Time airs on Sundays at 8/7c on ABC in the US. It will air on Channel 5 in the UK later this year.