John I, Duke of Brunswick-Grubenhagen
John I, Duke of Brunswick-Grubenhagen (born: before 1322; died: 23 May 1367)
was provost of the St. Alexandri Minster in Einbeck.
He was the son of Duke Henry
I "the Marvelous" of Brunswick-Grubenhagen and his wife Agnes of Meissen, daughter of Margrave Albert II of Meissen.
Ernest III, Duke of Brunswick-Grubenhagen
Ernest III of Brunswick- Grubenhagen- Herzberg( by a different counting: Ernest IV; 17 December 1518 in Osterode am Harz – 2 April 1567 in Herzberg Castle, Herzberg am Harz), was a member of the noble family of Guelph and a duke of Brunswick- Grubenhagen.
Ernest I, Duke of Brunswick-Grubenhagen
Ernest I of Brunswick- Grubenhagen( – 9 March 1361) was Prince of Brunswick- Grubenhagen.
Eric I, Duke of Brunswick-Grubenhagen
Eric I, Duke of Brunswick- Grubenhagen nicknamed" the winner"( – 28 May 1427), ruled the Principality of Grubenhagen, a part of the Duchy of Brunswick- Lüneburg.
William, Duke of Brunswick-Grubenhagen
William of Brunswick- Grubenhagen( – 1360) was a Prince of Brunswick- Grubenhagen.
Agnes of Meissen
Agnes of Meissen (born before 1264 – died after September 1332) was a noblewoman, the daughter of Albert II, Margrave of Meissen and his wife Margaret of Sicily.
Agnes was married with Henry I "the Marvelous" of Brunswick-Grubenhagen, in 1282.
They had 16 children:
Melchior of Brunswick-Grubenhagen
Melchior of Brunswick- Grubenhagen( died 1381 or 1384) was a German aristocrat, prince- bishop of Osnabrück from 1369, and then prince- bishop of Schwerin from 1376 to 1381.
He was the son of Henry II, Duke of Brunswick- Grubenhagen.
Henry IV, Duke of Brunswick-Grubenhagen
Duke Henry IV of Brunswick Grubenhagen( 1460 – 6 December 1526, Salzderhelden, now part of Einbeck) was a member of the Guelph dynasty and was Prince of Brunswick- Grubenhagen.
Anna of Brunswick-Grubenhagen-Einbeck
Anna of Brunswick- Grubenhagen- Einbeck( 1414 – 4 April 1474) was a daughter of Duke Eric I of Brunswick- Grubenhagen and his wife, Elisabeth of Brunswick- Göttingen.
Anna's first marriage was with Duke Albert III of Bavaria.
They had the following children:
After Albert's death, she married Duke Frederick III of Brunswick- Calenberg- Göttingen.
This marriage remained childless.
Clara of Brunswick-Wolfenbüttel
Clara of Brunswick- Wolfenbüttel( 16 November 1532 in Wolfenbüttel – 23 November 1595 at Herzberg Castle), was a princess of Brunswick- Wolfenbüttel by birth.
She was abbess of the secular Gandersheim Abbey and later Duchess of Brunswick- Grubenhagen by marriage.

Question: Who is the maternal grandmother of John I, Duke Of Brunswick-Grubenhagen?
Answer: Margaret of Sicily