"It's been so much fun just to see my mom happy," Kim Kardashian West tells PEOPLE exclusively. "My mom has had such a hard year and I think it's been refreshing to see her have a good time."
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"He's such a nice person," says Kim. "She can connect with him and go to the movies with him, work out with him. It's the little things."
As for the 25-year-age difference? Kim says she had a laugh when sister Kourtney, 36, posted a photo calling Corey a Grandpa (Kris has four young grandchildren Mason, 5, Penelope, 3, North, 2 and Reign, 11 months).
"She was like, 'Is this rude?'" says Kim. "And I'm like, no it's funny! He's young and he's a Grandpa!"
Keeping up with the Kardashians airs Sundays (9 p.m. ET) on E!
For much more from Kim Kardashian West, including details on her pregnancy and her family's turbulent year, pick up the new issue of PEOPLE, on stands Friday