MILWAUKEE: US Republican presidential candidate Mitt Romney likes to play the occasional prank on his staff. On Sunday, his aides got him back.

They made him victim of an elaborate April Fool's prank when he was introduced into an empty room, telling him beforehand, “We didn't get much of a turnout this morning.”

In on the joke were Wisconsin congressman Paul Ryan and Senator Ron Johnson, both of whom have endorsed Romney.

The prank was elaborate.

At a Milwaukee restaurant before a regularly scheduled campaign event, Romney was taken into a basement ballroom and his staff warned him in a holding room that the crowd was small.

“It's really small. But it'll be OK,'” Romney said they told him.

Ryan first went on stage and gave an entire introduction of Romney to the sound of applause piped in over the sound system.

Romney and Johnson then walked out and took their assigned places. The room was completely empty.

Romney said his first thought was, “This is going to look really bad on the evening news.”

The prank was a sign that Romney and his staff are feeling good about their prospects in the Wisconsin primary contest on Tuesday, and the overall state of the race. Romney leads Rick Santorum in Wisconsin polls and has a big lead in the state-by-state competition for the nomination.

Romney suggested payback might be in order.

“Not only did they do that but they caught it on camera,” said Romney. “This is known as forgive, but remember. We're going to remember this.”