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.
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.
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.
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 Alexandra of Baden
Princess Marie Alexandra of Baden(" Marie Alexandra Thyra Victoria Louise Carola Hilda"; 1 August 1902 – 29 January 1944) was a Hessian princess by marriage.
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 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.
Peter, Duke of Schleswig-Holstein
Peter, Duke of Schleswig- Holstein( 30 April 1922 in Schloss Louisenlund, Schleswig, Schleswig- Holstein, Germany – 30 September 1980 in Bienebek, Schleswig- Holstein, West Germany) was the Duke of Schleswig- Holstein and Head of both the House of Glücksburg and the entire House of Oldenburg from 10 February 1965 until his death on 30 September 1980.
Peter was the third and youngest son of Wilhelm Friedrich, Duke of Schleswig- Holstein and his wife, Princess Marie Melita of Hohenlohe- Langenburg.
He was a great- great- grandson of Queen Victoria through her second son, Prince Alfred.
Ernst Gunther, Duke of Schleswig-Holstein
Ernst Gunther, Duke of Schleswig- Holstein( August 11, 1863 – February 22, 1921) was a son of Frederick VIII, Duke of Schleswig- Holstein and Princess Adelheid of Hohenlohe- Langenburg.
He inherited his father's title as titular duke of Schleswig- Holstein.
On August 2, 1898 in Coburg, he married Princess Dorothea of Saxe- Coburg and Gotha, daughter of Prince Philipp of Saxe- Coburg and Gotha and Princess Louise of Belgium.
The grandfather of the bride, King Leopold II, did not attend the wedding but sent the Grand Cordon of the Order of Leopold as wedding gift.
The couple had no children.
However, on 11 November 1920, Ernst Gunther adopted Prince Johann Georg and his sister Princess Marie Luise, children of Prince Albrecht of Schleswig- Holstein- Sonderburg- Glücksburg.
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.

Question: Who is Princess Marie Alexandra Of Schleswig-Holstein's maternal grandfather?
Answer: Ernst II, Prince of Hohenlohe-Langenburg