Wiktionary
drop a bombshell
vb. (context idiomatic English) To announce surprising or alarming information suddenly and without warning.
Usage examples of "drop a bombshell".
Not until they were in their own solar chamber, however, did Angie drop a bombshell into their desultory and sleepy conversation.
Cascane commented with the studied calm of a man about to drop a bombshell.
Tricker, if you're going to drop a bombshell like this it might be best to make arrangements beforehand.
If a man wanted to drop a bombshell, there could scarcely be a better time to do it.