for a fact

I know for a fact that the readers will go for a draw here, but I am picking a winner.

For a fact, he knows the bench appeared in the movie.

"The gap Muhsin leaves is massive," she told the BBC, adding that she knew for a fact that there there were "a large number of queer Muslims around the world who are grief stricken".

I don’t want to say for a fact that the NSA doesn’t have a camera trained secretly on the whiteboard of, like, every mathematician in the world, because, who knows?

Although we know that American democracy has always been flawed and has never fully met its promise, most Americans still support this system of government and we know for a fact that they will protect it when they think it’s being challenged.