The announcement is the first royal decree of King Vajiralongkorn since he took the throne on December 1.
The decree said that Prem has fulfilled his duty as the regent of the country since the new king has ascended the throne and asked to resign from his previous position as chairman of the Privy Council. But King Vajiralongkorn decided to reappoint him to remain in office as Privy Council Chairman.
After King Bhumibol Adulyadej passed away on October 13, the then Crown Prince Vajiralongkorn asked for time to grieve his father before ascending the throne. Privy Council Chairman Prem then became the country's regent in line with Thailand’s Constitution.
The 96-year-old Prem is one of the most experienced and influential political figures in modern Thai history.
Prem served as the Prime Minister and stepped down in 1988. He has chaired the 19-member Privy Council of the king's official advisors since 1998.