Some of us in the press corps had thought it might be President Obama.
In recent days, Gibbs has been bringing a guest along to his briefings to take questions on the big issue of the day.
When the United Nations Security Council approved new sanctions against North Korea last Friday, Gibbs came to his daily briefing with United Nations Ambassador Susan Rice.
Two days earlier, as the deadline approached for the nation's TV stations to switch from analog to digital transmission, Gibbs surrendered the lectern to Secretary of Commerce Gary Locke, so he could take questions on the forthcoming changeover.
Other guest briefers to appear with Gibbs included Secretary of State Clinton and White House economist Jared Bernstein. And Gibbs had promised other guests in the days to come, and didn't rule out a visit by the top official in the U.S. government himself.
Today's schedule certainly lent itself to hopes of a surprise appearance by the president in the Briefing Room. He had no public appearances today until a big money Democratic fund-raiser tonight. Plus, there was lots to ask him about, including the situation in Iran, delays in getting his health care plan enacted and reports that the U.S. Navy was tracking a North Korean vessel suspected of carrying weapons or their parts.
In addition, word spread through the Press Room that two of the president's photographers were spotted in the Briefing Room as reporters prepared for their daily feeding of information.
In the minds of some, it added up to the possibility of a presidential appearance.
At CBS News, the bosses scrambled for the possibility of breaking into network programming should Barack Obama make an unexpected appearance before reporters.
Perhaps he had a surprise announcement to make, as he did on May 1st, when he unexpectedly interrupted spokesman Gibbs during a routine briefing to announce that Supreme Court Justice David Souter would be stepping down.
So there was a sense of anticipation as the announcement over the press room public address system proclaimed: "the briefing will begin in two minutes."
All eyes locked on the door from the lower press office through which Gibbs and his aides routinely walk. Would it open today for the president to walk in?
More than two minutes passed. And another two. And then another. Finally, the sliding door opened, but alas, no president. In walked Robert Gibbs and his team.
He sensed the disappointment.
'What?" he asked the press.
"We were wondering if there was a mystery guest," explained a reporter.
"No," said Gibbs, "None that I'm aware of."
"Bummer," was the unspoken reaction among the press.
Gibbs offered to re-stage his entry to the room, if reporters wanted to stand up and play out their hope that President Obama would enter.
To borrow a phrase associated with Mr. Obama, it was the "audacity of hope" that had reporters looking for something special on a slow Thursday at the White House.
But it proved to be hopes dashed. And spokesman Gibbs called on the Associated Press reporter, as usual, for the first question.