Question: Who is the paternal grandfather of Nguyễn Phúc Hồng Cai?

Knowledge 1: Nguyễn Phúc Hồng Cai
Nguyễn Phúc Hồng Cai (阮福洪侅, 13 December 1845 – 15 May 1876) was a prince of Nguyễn dynasty, Vietnam.He was the father of three emperors:Kiến Phúc, Đồng Khánh and Hàm Nghi.Hồng Cai was the twenty-sixth son of Thiệu Trị, and his mother was Trương Thị Vĩnh.He was a filial son and liked studying.He was granted the title Kiên Quốc Công (堅國公, "Duke of Kiên") in 1865.Tự Đức had no child, and adopted his two sons, Ưng Đăng and Ưng Thị, whom later became Emperor Kiến Phúc and Emperor Đồng Khánh respectively.Hồng Cai died in 1876 and received the posthumous name Thuần Nghị (純毅).He was buried in Hương Thủy.In 1885, Đồng Khánh ascended the throne, and granted him the title Kiên Vương (堅王, "Prince of Kiên") posthumously.Later, his title was elevated to Kiên Thái Vương (堅太王, "King Father Kiên") in 1888. [SEP] Knowledge 2: Thiệu Trị
Thiệu Trị (lit. "inheritance of prosperity"; 6 June 1807 – 4 November 1847), personal name Nguyễn Phúc Miên Tông or Nguyễn Phúc Tuyền, was the third emperor of the Nguyễn Dynasty.He was the eldest son of Emperor Minh Mạng, and reigned from 14 February 1841 until his death on 4 November 1847.
Knowledge 1: Nguyễn Phúc Hồng Cai
Nguyễn Phúc Hồng Cai (阮福洪侅, 13 December 1845 – 15 May 1876) was a prince of Nguyễn dynasty, Vietnam.He was the father of three emperors:Kiến Phúc, Đồng Khánh and Hàm Nghi.Hồng Cai was the twenty-sixth son of Thiệu Trị, and his mother was Trương Thị Vĩnh.He was a filial son and liked studying.He was granted the title Kiên Quốc Công (堅國公, "Duke of Kiên") in 1865.Tự Đức had no child, and adopted his two sons, Ưng Đăng and Ưng Thị, whom later became Emperor Kiến Phúc and Emperor Đồng Khánh respectively.Hồng Cai died in 1876 and received the posthumous name Thuần Nghị (純毅).He was buried in Hương Thủy.In 1885, Đồng Khánh ascended the throne, and granted him the title Kiên Vương (堅王, "Prince of Kiên") posthumously.Later, his title was elevated to Kiên Thái Vương (堅太王, "King Father Kiên") in 1888. [SEP] Knowledge 2: Tự Đức
Tự Đức( lit." inheritance of virtues", 22 September 1829 – 17 July 1883)( personal name: Nguyễn Phúc Hồng Nhậm, also Nguyễn Phúc Thì) was the fourth emperor of the Nguyễn dynasty of Vietnam; he ruled from 1847 to 1883.
Knowledge 1: Nguyễn Phúc Hồng Cai
Nguyễn Phúc Hồng Cai (阮福洪侅, 13 December 1845 – 15 May 1876) was a prince of Nguyễn dynasty, Vietnam.He was the father of three emperors:Kiến Phúc, Đồng Khánh and Hàm Nghi.Hồng Cai was the twenty-sixth son of Thiệu Trị, and his mother was Trương Thị Vĩnh.He was a filial son and liked studying.He was granted the title Kiên Quốc Công (堅國公, "Duke of Kiên") in 1865.Tự Đức had no child, and adopted his two sons, Ưng Đăng and Ưng Thị, whom later became Emperor Kiến Phúc and Emperor Đồng Khánh respectively.Hồng Cai died in 1876 and received the posthumous name Thuần Nghị (純毅).He was buried in Hương Thủy.In 1885, Đồng Khánh ascended the throne, and granted him the title Kiên Vương (堅王, "Prince of Kiên") posthumously.Later, his title was elevated to Kiên Thái Vương (堅太王, "King Father Kiên") in 1888. [SEP] Knowledge 2: Nguyễn Phúc Miên Định
Nguyễn Phúc Miên Định( 阮福綿定, 5 August 1810 – 5 November 1886), born Nguyễn Phúc Yến( 阮福宴), was a prince of Nguyễn dynasty, Vietnam.

Answer: Minh Mạng