I really can't understand how something like this could simply pop up out of the blue.
not anticipated; "unanticipated and disconcerting lines of development"- H W Glidden; "unforeseen circumstances"; "a virtue unlooked-for in people so full of energy"; "like a bolt out of the blue"
in a way that was not expected; "her brother showed up at the wedding out of the blue"
[ 'aut ] (adverb.) before 12th century. Middle English, from Old English ut; akin to Old High German uz out, Greek hysteros later, Sanskrit ud up, out.