Analysis of information sources in references of the Wikipedia article "จักรพรรดิตึ ดึ๊ก" in Thai language version.
[...] the Black Flags and their leader, Liu Yung-fu, were to acquire a certain dubious legitimacy and fame in the service both of the Vietnamese king, Tu Duc, and of the latter's Qing suzerains in their struggle against French imperialism in Tonkin.
{{cite web}}: ตรวจสอบค่าวันที่ใน: |accessdate= (help)[...] the Black Flags and their leader, Liu Yung-fu, were to acquire a certain dubious legitimacy and fame in the service both of the Vietnamese king, Tu Duc, and of the latter's Qing suzerains in their struggle against French imperialism in Tonkin.