Obama a surprise guest at his own party

Barack Obama just made a surprise appearance on stage after running mate Joe Biden's acceptance speech.

"Hello Democrats," he said. "I want to everyone to now understand why I am so proud to have Joe Biden.. and the entire Biden family with me on this journey to take America back."

"I think the convention's gone pretty well so far, what do you think?" he asked delegates, who answered with a resounding roar.

"If I'm not mistaken Hillary Clinton rocked the house last night," Obama said, also paying tribute to former President Bill Clinton's speech tonight.

The presidential nominee typically does not appear on stage until he accepts the nomination. But since he's making his speech at Invesco Field, this was his one and only appearance at the Pepsi Center in downtown Denver.

Obama then explained the move to the football stadium for his acceptance speech Thursday night, saying he wanted to open up the convention so everyone who wanted to could take part.