Kevin Costner Declares Himself a Swiftie, Raves About Taylor Swift Concert

Kevin Costner is a big-time Taylor Swift fan, and he doesn't care who knows it ... giving massive props to the singer after taking in one of her six record-setting shows in L.A.

TMZ broke the story -- Kevin was in a private suite Monday at SoFi Stadium with his daughter, Grace Avery, and a group of friends for Taylor's "Eras" tour.

The concert buzz was apparently still running through Costner Thursday when he jumped on his Instagram to rave about the show, posting a series of videos with the caption, “My videos are blurry, but I had an amazing time with my daughter at the Taylor Swift show. I was absolutely blown away watching her art bring so many people together.”

Remember, we got video of the "Yellowstone" star jamming along to "We Are Never Ever Getting Back Together" -- a fitting anthem given the nasty state of his ongoing divorce with Christine Baumgartner.

But, Kevin wasn't done there ... he also wrote of the show, “I had a great view of her band and had a blast watching them, too,” he added. “An inspiring night. I’m officially a Swiftie!”

Monday marked the first time we'd really seen Kevin let loose since Christine filed for divorce back in May -- ending their 18-year union which produced 3 kids.

Christine cited "irreconcilable differences" as the reason for the split -- and it was just last month when a judge ordered Costner to pay $129,755 in child support ... a bargain compared to the $248,000 Christine was asking he pony up.