Gossip Girl star Chace Crawford "is having a good time" with Carrie Underwood, his costar Nicole Fiscella told PEOPLE at Tiffany & Co.'s Blue Book Collection launch Saturday.

"They're the cutest couple," Fiscella says of the duo, who have been spotted hanging out around New York City in the last month, stopping by everywhere from hot spot Marquee to Justin Timberlake's Southern Hospitality restaurant.

"Chase is just such a great guy," Fiscella, 23, says of her costar, 22. "He's so fun and I think he just loves his life right now. He seems to be having a good time with [Carrie]."

And Underwood, 24, who told PEOPLE she found Crawford "really cute," has plans to meet Crawford's Gossip Girl costars. "We were all going to meet up one night and I didn't get to meet her yet," says Fiscella, "But I hear she's a great girl."