Japan's Princess Mako, the emperor's niece, has married her commoner college sweetheart on Tuesday and left the royal family after a years-long engagement beset by the scrutiny that has left the princess with post-traumatic stress disorder (PTSD).

Mako and fiance Kei Komuro, both 30, announced their engagement four years ago, a move initially cheered by the country. But things soon turned sour as tabloids reported on a money scandal involving Komuro's mother, prompting the press to turn on him.

The marriage was...