Suddenly and unexpectedly; without warning.
drop a bombshell
To announce surprising or alarming information suddenly and without wa…
all at once
Unexpectedly; without warning; all of a sudden.
out of the blue
Unexpectedly; without warning or preparation.
drop in
To arrive casually and unannounced, with little or no warning; also, t…
at a moment's notice
Immediately; instantaneously; without need of warning.
pop up
To appear without warning.