Come what come may
Let whatever events crop up come to pass.
From Shakespeare's Macbeth, 1605. Usually used just as 'come what may'.
A version of this was known in France as early as 1375, shown here from John Barbour's, The Bruce:
"Thai wuld defend, avalze que valze."
"avalze que valze" is "vaille que vaille" in modern French, meaning "let it avail what it may, come what may".
The Spanish "que sera sera" - "what will be, will be" is also old and predates Shakespeare's "come what come may".
The phrase, although it has those continental European counterparts, sounds archetypically English. It had reached the USA by 1878 though, when it appeared in the 4th Jan edition of The New York Times:
"...and should Parliament endorse that sentiment, come what come may, the might of England shall be put forth with a vigour and earnestness worthy of her old fame".
See other phrases and sayings from Shakespeare.