Kevin Costner Is the Life of the Party After 'Yellowstone' Death

Kevin Costner is living it up despite his character's suicide in "Yellowstone" ... partying and hobnobbing in New York City.

The "Yellowstone" star seemed full of life Monday at a shindig in the Big Apple ... smiling and laughing with other party guests, including track and field athlete Rainy Castaneda.

Kevin looked sharp with some thick black glasses and a goatee ... and everyone appeared to be having a great time.

"Yellowstone" fans aren't feeling the same way ... the show returned Sunday night, but Kevin's character was killed off in the first few minutes, sparking outrage.

Kevin confirmed in June he wasn't returning to the show but no one knew how his storyline would end ... and it turned out to be suicide.

Before the party, Costner went on a radio show Monday morning and said he was surprised by John Dutton's sendoff.