Hilton and Zylka, who have dated for two years, became engaged at the weekend while on a skiing trip.
And the ring - displayed in a photo posted on Hilton's Twitter account - is on the large side, to say the least.
Hilton wrote: "I have never felt so happy, safe and loved. He is perfect for me in every way and showed me that fairytales really do exist!"
The couple were on a trip to Aspen, Colorado, when Zylka got down on one knee and popped the question.
Zylka, who starred in US drama The Leftovers, first met Hilton eight years ago.
Hilton told US magazine People that the engagement ring is "so gorgeous and sparkling".