Princess Alexandra Victoria of Schleswig-Holstein-Sonderburg-Glücksburg
Princess Alexandra Victoria of Schleswig-Holstein- Sonderburg- Glücksburg( 21 April 1887 – 15 April 1957) was a daughter of Friedrich Ferdinand, Duke of Schleswig- Holstein and his wife Princess Karoline Mathilde of Schleswig- Holstein- Sonderburg- Augustenburg.
Joachim Frederick, Duke of Schleswig-Holstein-Sonderburg-Plön
Joachim Frederick of Schleswig-Holstein- Sonderburg- Plön( 9 May 1668, Magdeburg – 25 January 1722, Plön), also known as Joachim Frederick of Schleswig- Holstein- Plön, was the third Duke of Schleswig- Holstein- Plön, a dukedom created by the division of the Duchy of Schleswig- Holstein- Sonderburg.
Albert, Duke of Schleswig-Holstein
Albert, Duke of Schleswig- Holstein( Albert John Charles Frederick Alfred George; 26 February 1869 – 27 April 1931), was a grandson of Queen Victoria.
He was the second son of Victoria's daughter, Princess Helena, by her husband Prince Christian of Schleswig- Holstein.
He was the head of the House of Oldenburg and also the House of Schleswig- Holstein- Sonderburg- Augustenburg and the Duke of Schleswig- Holstein between 1921 and 1931.
Friedrich Ferdinand, Hereditary Prince of Schleswig-Holstein
Friedrich Ferdinand, Hereditary Prince of Schleswig- Holstein( born 19 July 1985 in Eckernförde, Schleswig- Holstein, West Germany) is the heir apparent of Christoph, Prince of Schleswig- Holstein, current head of the House of Schleswig- Holstein, the senior extant line of the House of Oldenburg.
Friedrich Ferdinand is the eldest son of Christoph and his wife Princess Elisabeth of Lippe- Weissenfeld.
As a 4 th- great- grandson of Queen Victoria, he is in the line of succession to the British throne.
He is heir- apparent to the headship of a house that includes the Queen of Denmark, the King of Norway, the deposed King of Greece and, patrilineally, the Prince of Wales.
He is styled as" His Highness the Hereditary Prince of Schleswig- Holstein".
Friedrich Ferdinand, Duke of Schleswig-Holstein
Friedrich Ferdinand of Schleswig- Holstein- Sonderburg- Glücksburg( 12 October 1855 – 21 January 1934) was the fourth Duke of Schleswig- Holstein- Sonderburg- Glücksburg and became Duke of Schleswig- Holstein in 1931.
Princess Marie Melita of Hohenlohe-Langenburg
Princess Marie Melita of Hohenlohe-Langenburg (18 January 1899, Langenburg, Württemberg – 8 November 1967, Munich, Germany) was the Duchess consort of Schleswig-Holstein as the wife of Wilhelm Friedrich, Duke of Schleswig-Holstein.
She was the eldest daughter of Ernst II, Prince of Hohenlohe-Langenburg and his wife Princess Alexandra of Saxe-Coburg and Gotha.
Wilhelm Friedrich, Duke of Schleswig-Holstein
Friedrich, Duke of Schleswig- Holstein- Sonderburg- Glücksburg, from 1934 Duke of Schleswig- Holstein( 23 August 1891 – 10 February 1965), was the Duke of Schleswig- Holstein and Head of the House of Oldenburg from 21 January 1934 until his death on 10 February 1965.
Joachim Ernest, Duke of Schleswig-Holstein-Sonderburg-Plön
Joachim Ernest of Schleswig-Holstein- Sonderburg- Plön( 29 August 1595 – October 5, 1671), also" Joachim Ernest of Schleswig- Holstein- Plön", was the first Duke of Schleswig- Holstein- Sonderburg- Plön, which emerged from a division of the Duchy of Schleswig- Holstein- Sonderburg.
Princess Marie Alexandra of Schleswig-Holstein
Princess Marie Alexandra of Schleswig-Holstein -Sonderburg- Glücksburg, since 1941 of Schleswig- Holstein( Marie Alexandra Caroline- Mathilde Viktoria Irene; 9 July 1927, Schloss Louisenlund, Schleswig, Schleswig- Holstein, Germany – 14 December 2000, Friedrichshafen, Baden- Württemberg, Germany) was a member of the House of Schleswig- Holstein- Sonderburg- Glücksburg.
Marie Alexandra was the fourth and youngest child of Wilhelm Friedrich, Duke of Schleswig- Holstein and his wife Princess Marie Melita of Hohenlohe- Langenburg.
Her older brother Peter was the Duke of Schleswig- Holstein and Head of the House of Oldenburg from 10 February 1965 until his death on 30 September 1980.
Hans Albrecht, Hereditary Prince of Schleswig-Holstein
Hans Albrecht, Hereditary Prince of Schleswig-Holstein-Sonderburg-Glücksburg, since 1931 of Schleswig-Holstein (12 May 1917, Schloss Louisenlund, Schleswig, Schleswig-Holstein, Germany – 10 August 1944, Zedlinsk, Poland) was the Hereditary Prince of Schleswig-Holstein and the heir apparent to the Head of the House of Oldenburg.
Hans Albrecht was the eldest son of Wilhelm Friedrich, Duke of Schleswig-Holstein and his wife Princess Marie Melita of Hohenlohe-Langenburg.
The Hereditary Prince fought in the Second World War between 1939 and 1944 when he died from wounds received in action near Zedlinsk, Poland.

Question: Who is Hans Albrecht, Hereditary Prince Of Schleswig-Holstein's maternal grandmother?
Answer: Princess Alexandra of Saxe-Coburg and Gotha