flabbergastingly

It was a good date but the food at the restaurant was so flabbergastingly excellent I could barely think of anything else to talk about.

He had said he would clean his room a thousand times before, but this time he actually did it, and flabbergastingly well too.

1922, George Jean Nathan, Henry Louis Mencken. The smart set: a magazine of cleverness, Volume 69. Ess Ess Pub. Co. page 49. (There) must be sympathy in the back parlor if it is to get its message across, and that this flabbergastingly important message... is as follows:...