The home and garden guru shared her thoughts on one of Hollywood's biggest romances after spending time with the couple at the White House Correspondents' Dinner in April.
She told E! News: "They seem to have a nice affection for one another, which is so nice."
Stewart also commented on the unexpected nature of Kardashian, 41, and Davidson's connection, saying they're "an unlikely pairing and much, much more unlikely than my steak tartare and Ruffles potato chips."
Davidson, 29, and Kardashian sparked romance rumors in October after they were spotted holding hands on a roller coaster.
While the pair were initially said to be just friends, their hangouts after Kardashian hosted SNL eventually turned romantic, and Davidson first referred to Kardashian as his "girlfriend" in a conversation with PEOPLE in February.
Stewart spent even more time with members of the Kardashian/Jenner family this year. She surprised Khloé Kardashian with the help of Kris Jenner in March. After having lunch together at Jenner's home, the family matriarch posted an Instagram thank you to Stweart.
"How do I say thank you for coming to the house and helping me surprise @khloekardashian??!!!!!! You are someone I have truly looked up to and admired for so many years!!!" Jenner wrote. "You have been such an inspiration to me in so many ways!"
Stewart reflected on the lunch date with the girls, and one of Jenner's best-kept rooms. "She had a very well-stocked library, that was very interesting," Stewart said. "I said, 'Well, have you read all these books'? And she said no, she bought the entire library from a friend who was moving and she just bought all the books. And she said her dream is to sit down one day and have time to read them all, which is a very, very nice life goal."
Of lunch, she added, "She has a chef and we had a lovely lunch. Of course, they don't eat very much. They are careful about their diet. I ate!"