Saisanee Wongsuwon, the mother of Deputy Prime Minister Prawit Wongsuwon, died of chronic kidney disease at King Mongkut Hospital on Tuesday night. She was aged 99 years.
Close aides said Gen Prawit had visited his mother at the hospital almost everyday before she passed away at 10.32pm.
A royally-sponsored bathing rite will be held on Thursday at 5pm at Sala 5, Wat Somanas Rajavaravihara in Pom Prap Sattru Phai district, Bangkok.
Evening prayer will be held for seven days. She will be cremated in 100 days.
Saisunee was married to Maj Gen Prasert Wongsuwon. They had five sons: Gen Prawit, Adm Sitthavach, Pol Gen Patcharawat, Pongphan (deceased) and Phanpong.
When Maj Gen Prasert died in 1985, Gen Prawit assumed the role of "big brother", taking care of his mother and younger brothers.
On Wednesday morning, Gen Prawit was scheduled to attend the House meeting. At 10am, he was scheduled to chair a meeting of the committee for the conservation and development of Rattanakosin and the Old City at Government House.