It won't be a very happy 21st birthday today for Tara Conner: The Kentucky beauty is on the verge of losing her Miss USA crown over allegations of drug use and excessive partying, and sources tell TMZ she will be replaced tomorrow officially by Tamiko Nash, Miss California.

The damning evidence continues to mount against Conner, whose tumultuous reign began in April. Yesterday, the New York Daily News reported that Conner had failed a drug test for cocaine. Sources confirm to TMZ that after she was "caught red-handed," she took a hair follicle drug test that returned positive for coke.