blurt out
To say something unexpectedly, often at an inopportune time or with the wrong audience (as of a private or secret matter). A noun or pronoun can be used between "blurt" and "out." I can't believe you blurted out the plans for her surprise party right to her face! Don't tell your little brother anything you want to keep secret, because he'll definitely blurt it out.
blurt something out (at someone)
to say something to someone without thinking. (Usually to say something that should not be said.) It was a secret. Why did you blurt it out? Why did you blurt out our hiding place?
blurt out
Say abruptly or inadvertently, utter without thinking. For example, Unfortunately he blurted out how much he hated formal dinners just as his hostess walked in . [Late 1500s]