In a way that was not expected.

synoniem: out of the blue.

Roget 132: early, soon, anon, betimes, rath^†; eft, eftsoons; ere long, before long, shortly; beforehand; prematurely etc. adj.; precipitately etc. (hastily) 684; too soon; before its time, before one's time; in anticipation; unexpectedly etc. 508.    suddenly etc. (instantaneously) 113; before one can say 'Jack Robinson'," at short notice, extempore; on the spur of the moment, on the spur of the occasion [Bacon]; at once; on the spot, on the instant; at sight; offhand, out of hand; a' vue d'oeil [Fr.]; straight, straightway, straightforth^†; forthwith, incontinently, summarily, immediately, briefly, shortly, quickly, speedily, apace, before the ink is dry, almost immediately, presently at the first opportunity, in no long time, by and by, in a while, directly.    ... meer laten zien

Roget 508: abruptly, unexpectedly, surprisingly; plump, pop, a l'improviste [Fr.], unawares; without notice, without warning, without a 'by your leave';" like a thief in the night, like a thunderbolt; in an unguarded moment; suddenly etc. (instantaneously) 113.    ... meer laten zien

Without advance planning.

synoniemen: accidentally, by chance, circumstantially.