Natthawut said Boon-ua died at 8 am of natural causes.
A bathing rite will be held at 4 pm at Wat Thepsirinthawas and a royally-sponsored bathing rite will be held at 5 pm. Praying rite will be held at 7 pm starting from Friday.
Boon-ua became the 19th House speaker of Thailand in 1995 and became the 23th Parliament president from July 11 1995 to September 27 1996.