The actor-model was previously engaged to model Hanna Beth, but they split in 2015.
He also dated Pretty Little Liars actress Lucy Hale.
Zylka, 31, was also engaged in the past to model Hanna Beth.
The two split in 2015, when Chris blasted her on social media for "backstabbing" him.
"My #Valentine," Hilton captioned a photo of herself and Zylka for her 6.6 million followers. "Happy Birthday @Paris Hilton Can't wait to celebrate with you soon! I have known you since you were born and you have grown up to be an amazing young lady..
"The best feeling is when someone looks at you like you are magic..." she added to another. smart, kind, beautiful inside and out and always thinking of others," Kardashian's mom, Kris Jenner, added on Instagram.
“They are head over heels for each other, they have never been happier and they make the perfect couple," a source close to the duo tells Us Weekly.Hilton confirmed to Too Fab that the two were very much an item on Sunday night at 2017 Hollywood Beauty Awards."Never been happier," she responded as she got into her car.] Paris hasn't really been cozying to any guys lately…
Paris Hilton and her boyfriend, Thomas Gross, have split after a year of dating, a source confirms to Us Weekly.
"I'm so busy with my work that when I do get time at home, I don't have time to watch reality TV.