This national holiday celebrates the birthday of Yang Di Pertuan Agong, the King and head of state of Malaysia.
The date of this holiday is ceremonial and may change depending on the birthday of the current King. In 2017, the date was changed from the first Saturday in June to the last Saturday in July following the installation of His Majesty the 15th Yang Di Pertuan Agong, Sultan Muhammad V.
In 2017, a further amendment changed the date to September 9th 2017. Though not stated, this change looked like it meant observation on September 9th would stay in place during the reign of Sultan Muhammad V.
In 2019, the holiday remained on September 9th. In 2020, it was to be observed on the first Saturday in June, June 6th; however, in March 2020, it was announced that the holiday would move to Monday June 8th 2020 and that it will be henceforth be observed on the first Monday in June.
Source By OfficeHoliday