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.