"The ring was so gorgeous and sparkling. I was shaking as I put it on. It is the most beautiful ring that I have ever seen."
The 32-year-old actor said he cannot wait to spend the rest of his life with the socialite, who he described as his "dream girl".
He said: "Paris is the most beautiful and incredible woman both inside and out.
"I feel like the luckiest man in the world to be marrying my dream girl. I can't wait to spend the rest of our lives together."
Hilton and The Leftovers star Zylka first met at an Academy Awards party eight years ago but were reunited two years ago, and she confirmed their relationship on her Instagram page in February 2017.
In November, the businesswoman said Zylka was "everything [she's] ever wished for" and was glad he saved her from "all these weirdos".
She said: "We are so perfect together. He's my everything. I'm so happy and excited to have someone who is my best friend, who I trust. Everything I've ever wished for came true.
"I always thought I would end up alone just because I never thought I would fall in love and trust somebody. With him, it's like God literally made him for me to save me from all these weirdos."