The baby bump is for real.
"Don't worry Dave, it's not yours," the pop princess quipped.
The revelation ended weeks of speculation in entertainment magazines, which have been regularly publishing pictures of Spears' apparently expanding waistline.
Spears, 24, and her husband, backup dancer-turned-rapper Kevin Federline, 28, were married in 2004 and have an 8-month-old son, Sean Preston.
Federline also has two children, Kori and Kaleb, with his former girlfriend, Shar Jackson.
Spears rose to fame at 16 with a naughty schoolgirl image and the multiplatinum album "... Baby One More Time."