Keywords: show up, pop up, unexpected
As a Noun
Something that happens unexpectedly or without warning.
As a Verb or Adjective
To happen suddenly or as a surprise. English = (be) unexpected.
To appear in a place unexpectedly or to attend an event unexpectedly or without having been invited. Idiomatic English = show up, pop up.
Used next to a verb to mean the action happens suddenly and as a surprise. English = unexpectedly.