Gerhard I, Count of Holstein-Itzehoe
Gerhard I, Count of Holstein- Itzehoe( 1232 – 21 December 1290) was the only count of Holstein- Itzehoe.
Ingeborg of Mecklenburg-Schwerin
Ingeborg of Mecklenburg( 1343/45 – 25 July 1395) was a daughter of Albert II, Duke of Mecklenburg and his wife, Euphemia of Sweden.
Euphemia was a daughter of Ingeborg of Norway, who was the only legitimate child of King Haakon V of Norway.
Thus, Ingeborg of Mecklenburg was Haakon V's great- granddaughter.
In 1360, she married Louis VI" the Roman" of Bavaria; she was his second wife.
The marriage remained childless.
After Louis's death, she married Henry II, Count of Holstein- Rendsburg.
They had at least four children:
Ingeborg of Holstein
Ingeborg of Holstein (1396 – 14 October 1465), was Abbess of Vadstena Abbey 1447-1452 and 1457-1465.
She was the daughter of Gerhard VI, Count of Holstein-Rendsburg (d. 1404) and Catherine Elisabeth of Brunswick-Lüneburg.
In 1408, she was placed in the convent by Queen Margaret I of Denmark by special consent of the Pope.
She became a full member of the order in 1415.
Due to her age, it is believed that she initially resided in her own house on the convent premises.
In 1447, she was appointed Abbess.
Her election was controversial and an active opposition remained against her appointment.
She had the loyal support of the confessor of the abbey, Magnus Unnonis.
Ingeborg was the maternal aunt of King Christian I of Denmark, which was likely the cause to why King Charles VIII of Sweden 25 April 1452
demanded that she and the confessor of the abbey, Magnus Unnonis, should be deposed.
Bishop Nils König of Linköping saw no cause for this, but both Ingeborg and Unnonis stepped down in
May. They were reinstated in their positions in 1457.
Ingeborg worked to install the so-called vårfrupenningen to a regular fee, a goal she succeeded with by permission of Charles VIII of Sweden in 1450, and again from Christian I of Denmark in 1461.
In 1462, she received the papal legate Marinus de Fregeno in Vadstena.
Upon the request of Christian I, she wrote the (C 50, UUB), "Fjorton råd om ett gudeligt leverne" (Fourteen Advises to live goodly), likely before his visit in 1461.
Ingeborg is believed to have supported the Roman side against Conciliarism and the new Papal policy of Concords and diplomacy, and opposed the national centralism of Charles VIII of Sweden.
Adolph V, Count of Holstein-Segeberg
Adolph V, Count of Holstein- Segeberg( – 1308) was the ruling count of Holstein- Kiel from 1263 to 1273 and of Holstein- Segeberg from 1273 until his death.
Ingeborg of Sweden (1263–1292)
Ingeborg of Sweden( 1263–1292), was a Swedish Princess and Countess consort of Holstein- Plön by marriage to Gerhard II, Count of Holstein- Plön.
She was the daughter of Valdemar, King of Sweden, and Sophia of Denmark.
Catherine Elisabeth of Brunswick-Lüneburg
Catherine Elisabeth of Brunswick-Lüneburg (ca 1367 – after 1423) was Duchess consort of Schleswig and Countess consort of Holstein-Rendsburg.
She was the regent of some of the fiefs of her son Henry during his minority from 1404 to 1415.
She was a daughter of Magnus II, Duke of Brunswick-Lüneburg and Catherine of Anhalt-Bernburg, daughter of Bernhard III, Prince of Anhalt-Bernburg.
Through her mother, she was the great-great granddaughter of King Abel of Denmark.
She would also become the grandmother of Christian I of Denmark.
Catherine Elisabeth was in fact likely named only Catherine; she was often referred to as Elisabeth in older literature, but this was likely due to a mixup with her younger sister, who was named Elisabeth.
In the 14th century, it was still rare to have two first names such as "Catherine Elisabeth".
Due to this confusion, however, she has sometimes been referred to by both names.
John Adolf, Duke of Holstein-Gottorp
Johann Adolf of Holstein- Gottorp( 27 February 1575 – 31 March 1616) was a Duke of Holstein- Gottorp.
Albert II, Count of Holstein-Rendsburg
Albert II of Holstein( – 28 September 1403 in Dithmarschen( Ditmarsh)) was the ruling Count of Holstein- Rendsburg from his father's death, in 1381 or 1384, until 1397.
From 1397 until his death, he was Count of Holstein- Segeberg.
Henry I, Count of Holstein-Rendsburg
Henry I, Count of Holstein- Rendsburg( 1258–1304) was the first Count of Holstein- Rendsburg.
Christian August of Holstein-Gottorp, Prince of Eutin
Christian August of Holstein-Gottorp-Eutin (11 January 1673 – 24 April 1726) was a cadet of the reigning ducal House of Holstein-Gottorp who became prince of Eutin, prince-bishop of Lübeck and regent of the Duchy of Holstein-Gottorp.
He was the father of Adolf Frederick, King of Sweden, and the maternal grandfather of Catherine the Great, Empress of Russia.

Question: Who is Ingeborg Of Holstein's maternal grandfather?
Answer: Magnus II, Duke of Brunswick-Lüneburg