Maximilian I, Prince of Hohenzollern-Sigmaringen
Maximilian I, Prince of Hohenzollern- Sigmaringen( 20 January 1636 – 13 August 1689 in Sigmaringen) was a German nobleman.
He was the third ruling Prince of Hohenzollern- Sigmaringen; he ruled from 1681 until his death.
Constantine, Prince of Hohenzollern-Hechingen
Constantin, Prince of Hohenzollern- Hechingen( Friedrich Wilhelm Konstantin Hermann Thassilo; 16 February 1801 – 3 September 1869), was the last Prince of Hohenzollern- Hechingen.
Constantine was the only child of Frederick, Prince of Hohenzollern- Hechingen and his wife, Princess Pauline of Courland, the daughter of the last Duke of Courland, Peter von Biron.
Prince Karl Anton of Hohenzollern
Prince Karl Anton of Hohenzollern- Sigmaringen( 1 September 1868 – 21 February 1919) was a member of the Princely House of Hohenzollern- Sigmaringen.
Karl Anton was the third and youngest son of Leopold, Prince of Hohenzollern and his wife Infanta Antónia of Portugal.
Karl Anton's elder brothers were William, Prince of Hohenzollern and Ferdinand I of Romania.
Elisabeth of Brandenburg, Duchess of Brzeg-Legnica and Cieszyn
Elisabeth of Hohenzollern( 1 May/ 29 September 1403 – 31 October 1449), was a German princess member of the House of Hohenzollern and by her two marriages Duchess of Brzeg- Legnica and Cieszyn.
She was the eldest daughter of Frederick I, Elector of Brandenburg by his wife Elisabeth, daughter of Frederick, Duke of Bavaria- Landshut.
Alexander, Hereditary Prince of Hohenzollern
Alexander, Hereditary Prince of Hohenzollern( born 16 March 1987 in New York City) is a member of the Princely House of Hohenzollern.
Alexander is the eldest son of Karl Friedrich, Prince of Hohenzollern and Countess Alexandra Schenck von Stauffenberg, who divorced in 2010.
He is the heir apparent to the headship of the princely house.
Friedrich Wilhelm, Prince of Hohenzollern
Friedrich Wilhelm, Prince of Hohenzollern( 3 February 1924 – 16 September 2010) was the head of the Princely House of Hohenzollern for over 45 years.
Frederick, Prince of Hohenzollern
Frederick, Prince of Hohenzollern  (30 August 1891 in Heiligendamm, Mecklenburg-Schwerin – 6 February 1965 in Krauchenwies, Baden-Württemberg, Germany) was the eldest son of William, Prince of Hohenzollern and Princess Maria Teresa of Bourbon-Two Sicilies.
He had a twin brother, Franz Joseph, Prince of Hohenzollern-Emden, who was born a few minutes after he was.
William, Prince of Hohenzollern
William, Prince of Hohenzollern  (7 March 1864 in Schloss Benrath, near Düsseldorf – 22 October 1927 in Sigmaringen) was the eldest son of Leopold, Prince of Hohenzollern and Infanta Antónia of Portugal.
William was an older brother of Ferdinand of Romania.
His maternal first cousins included (among others)
Carlos I of Portugal, Infante Afonso, Duke of Porto, Frederick Augustus III of Saxony, and Princess Maria Josepha of Saxony.
Between 1880 and 1886, William was heir presumptive to the Romanian throne.
On 20 December 1886, he renounced his rights to the throne in favor of his brother Ferdinand.
Karl Friedrich, Prince of Hohenzollern
Karl Friedrich, Prince of Hohenzollern( born 20 April 1952) is the eldest son of the late Friedrich Wilhelm, Prince of Hohenzollern and Princess Margarita of Leiningen.
He became head of the Princely House of Hohenzollern, the Roman Catholic Swabian branch of the dynasty, upon his father's death on 16 September 2010.
Frederick XI, Count of Hohenzollern
Friedrich XI, Count of Hohenzollern( died 26 November 1401), nicknamed" Friedrich the Elder" was a German nobleman.
He was a member of the House of Hohenzollern and a ruling Count of Hohenzollern- Hechingen.

Question: Who is the paternal grandfather of Frederick, Prince Of Hohenzollern?
Answer: Leopold, Prince of Hohenzollern