Celeb attorney Gloria Allred showed up to the Spears/Federline hearing with her "secret witness", whom X17 id'd as Brit's former bodyguard Tony! Gloria said her client, who allegedly has damning information on how Britney handled her kids, was there to testify on the custody issue.

So why didn't Brit's attorney call on another former bodyguard who would support her case? Because, according to an X17 source, Tony is not a credible witness and Brit's not worried! He was fired by Britney because it took him "10 mins to get in and out of a car, and he would start so much chaos everywhere they went, she got sick of him!"

Stay tuned to X17, -- more info coming when the hearing wraps up!