Carrie Underwood is a dog's best friend! On Saturday (March 8), the star singer was the surprise special guest at the Oklahoma Alliance for Animals (OAA) Fur Ball benefit.

Underwood's appearance was a personal one, as she was there to cheer on a shelter from her hometown that was being honored. Of course, the country singer wasn't the only famous figure to make an appearance at the OAA's annual fundraiser -- she was joined by Platty, a local rescued dog who has garnered international attention due to a tumor on his face that gives him the appearance of a platypus.

More than 300 people came out for the big night ... and that was before they knew the country sweetheart would be there!

“It was excellent. I can’t say it could have gone any better," OAA president Jamee Suarez says, adding that they had to keep Underwood's attendance under wraps before the evening took place. "There's no place big enough ... for everybody had they known she would be coming."

Along with a photo opp with Platty, Underwood posed for pictures with guests and even sang 'Happy Birthday' to Suarez.

The Oklahoma Alliance for Animals is a Tulsa-based nonprofit organization with the mission of reducing pet overpopulation, encouraging responsible pet ownership and promoting the humane treatment of animals through community collaboration and education.

It's no secret that Underwood and her husband, hockey star Mike Fisher, are big animal lovers. The Nashville power couple have two dogs of their own -- Penny and Ace -- and are constantly highlighting them on social media. Just last week, Underwood posted this adorable video with her "navigator" Penny on Twitter.