21 ตุลา เราไม่ลืมสมเด็จย่า .. HRH PRINCESS MOTHER .. Her Royal Highness Princess Srinagarindra, the Princess Mother

http://en.wikipedia.org/wiki/Srinagarindra -a patite IRON LADY of the world

• 21 October 1900 – 17 August 1913; Miss Sangwan  
• 17 August 1913 – 10 September 1920; Miss Sangwan Talapat
• 10 September 1920 – 16 November 1938; Mom Sangwan Mahidol na Ayudhya
• 16 November 1938 – 9 June 1970; Princess Mother Sri Sangwan
• 9 June 1970 – 18 July 1995; Her Royal Highness Princess Srinagarindra, the Princess Mother

There is some confusion as to why the Princess Mother was never titled Queen Mother, considering that she was the mother of two kings. Since her husband was never king and only had the title of a prince, she never ascended as a queen-consort, and was therefore she was given the title Princess Mother by her son.
courtesy: http://en.wikipedia.org/wiki/Srinagarindra