Japanese media say the palace has announced that Princess Mako's wedding will be postponed.
Mako and her college classmate Kei Komuro announced their engagement last September. Mako is Emperor Akihito's oldest grandchild.
According to Japanese media, the Imperial Household Agency said Tuesday that the wedding, planned for November, will be delayed until 2020, citing lack of time for preparations.
The media quoted Mako as saying in a statement that the couple decided to postpone the wedding until after the emperor's abdication next year.
The sudden announcement triggered speculation that the postponement may be linked to recent tabloid bashing on Komuro's family background.
The 84-year-old Akihito is set to abdicate April 30 next year, with Crown Prince Naruhito succeeding him on the Chrysanthemum throne the next day.