Katy Perry's 28th birthday got off to a good start on Wednesday (24Oct12) after U.S. President Barack Obama gave her an "unforgettable" shout-out at a campaign rally in Las Vegas.

The California Gurls hitmaker, who turns 28 on Thursday (25Oct12), showed her support for the Democratic candidate by wearing a ballot-inspired latex dress to perform at the America Forward fundraiser in Sin City, where she had the chance to introduce her 91-year-old grandmother Ann Hudson to the President.

Obama later told the crowd, "I am so grateful to Katy Perry for the unbelievable performance.

"Getting to know Katy, she's just a wonderful young lady, and I can tell that part of it is because of her outstanding grandma Ann, a 50-year resident of Nevada, so give her a big round of applause".

Perry later took to Twitter.com to share her delight, writing, "So tonight was a great night!

"The President gave grandma and I unforgettable shout outs and now I am officially 28! Best. Birthday. Ever".