Princess Mako, the eldest granddaughter of Emperor Akihito, and her longtime boyfriend Kei Komuro will be formally engaged in March in a traditional court ceremony, an Imperial Household Agency source said Tuesday.

The traditional rite of betrothal called Nosai no Gi is slated for March 4, which falls on a Sunday. The wedding ceremony is expected to take place next fall, the source said.

During the March ceremony, a messenger from Komuro will visit the princess' Imperial residence with gifts including sake, sea bream and textiles to formally convey the proposal. The date of the wedding will be fixed after the ceremony.