If you say that someone's behaviour is a volte-face, you mean that they have changed their opinion or decision completely, so that it is the opposite of what it was before. The day's events were a remarkable volte-face. = about-face. a change to a completely opposite opinion or plan of action = U-turn
a reversal in attitude or principle or point of view; "an about-face on foreign policy"
Shakespeare often used volte faces in the rhyming couplets at the end of his sonnets.
about-face, act of turning to face the opposite direction from the original position (Military); complete change in position or attitude; sudden reversal in opinion or policy