1
general::
A misfortune that unexpectedly turns into good fortune, as in Missing the train was a blessing in disguise, for if I hadn't, I wouldn't have met my future wife. [Mid-1700s]
American Heritage Idioms
2
general::
Phrase(s): a blessing in disguise
Fig. something that at first seems bad, but later turns out to be beneficial. • Tony’s motorcycle accident was a blessing in disguise, because he got enough insurance money from the other driver to make a down payment on a house. • Dad’s illness was a blessing in disguise; it brought the family together for the first time in years.
McGrawhill's American Idioms And Phrasal Verbs