William, Duke of Saxe-Weimar
Wilhelm, Duke of Saxe-Weimar (Altenburg, 11 April 1598 – Weimar, 17 May 1662), was a duke of Saxe-Weimar.
Wilhelm was the fifth (but third surviving) son of Johann, Duke of Saxe-Weimar, and Dorothea Maria of Anhalt.
He was brother to Bernard of Saxe-Weimar, a successful Protestant general in the Thirty Years' War, and to Ernest I, Duke of Saxe-Gotha (later Altenburg), a successful and well regarded ruler known as "The Pious".
John Ernest, Duke of Saxe-Eisenach
Johann Ernst of Saxe-Eisenach (Gotha, 9 July 1566 – Eisenach, 23 October 1638), was a duke of Saxe-Eisenach and later of Saxe-Coburg.
He was the fourth (but second surviving) and youngest son of Johann Frederick II, Duke of Saxony and Countess Palatine Elisabeth of Simmern-Sponheim.
His grandfather, Johann Frederick I, had still held the title of Elector of Saxony, but after the Battle of Mühlberg he lost the title to his cousin Maurice, from the Albertine line.
His father tried since then to regain the Electorate again for the Ernestine line.
For this purpose he accepted an outlawed knight, Wilhelm von Grumbach, with himself, which led finally to the fact that also over his father the anger of the Emperor.
Only one year after his birth was besieged the castle of his father in Gotha by troops of the Elector Augustus of Saxony and finally conquered.
His father came into imperial prison from the rest of his life.
His mother, Johann Ernst and his older brothers had to flee from Gotha.
They found first admission with his uncle, the duke Johann Wilhelm of Saxe-Weimar, who took over also the guardianship for the princes -at the same time, he was granted by the Emperor with the lands of his brother Johann Frederick II-.
After a short time in Weimar, Johann Ernst, as well as his mother and his brothers, lived in Eisenach and Eisenberg.
Later, his uncle Johann Wilhelm of Saxe-Weimar lost the Imperial favour.
In the Diet of Speyer (1570), the Emperor decided to restore to the three sons of Johann Frederick II his hereditary rights.
In 1572 his older brother Frederick Heinrich died from typhus fever.
The same year, by the Division of Erfurt, the decision of the Diet of Speyer was made: The lands of his father were extracted again from the duchy of Saxe-Weimar, and created from them the new "Duchy of Saxe-Coburg-Eisenach".
Johann Ernst and his older surviving brother, Johann Casimir, were made rulers of the new country.
During there minority, the lands were under the guardianship of the three Elector Princes: Frederick III of the Palatinate (also his maternal grandfather), Johann George of Brandenburg and Augustus of Saxony; also, they took the regency over Saxe-Coburg-Eisenach.
The duchess Elizabeth moved to Austria, where she should live themselves in the future in the proximity of her husband, still imperial prissioner.
The two young princes, Johann Casimir and Johann Ernst, moved to Coburg, the future residence of his new principality.
With only six years, Johann Ernst was separated from his parents forever and entrusted to the education of strange persons.
Since 1578 he visited the University of Leipzig then together with his brother.
In 1586, after the wedding of his brother with Anna of Saxony, the daughter of the Elector Augustus, the guardianship finalized, and Johann Casimir began, together with his brother, the independent ruling of Saxe-Coburg-Eisenach.
Johann Casimir and Johann Ernst governed together the principality for the next ten years; however, Johann Casimir carried the main responsibility for the government as an older brother.
Also, in order to had a separated residence from his brother too, Johann Ernst establishes himself in the small town of Marksuhl on 1587.
Since 1590 Johann Ernst withdrew himself from the government of the duchy, with his brother completely agreed it, that this should govern the duchy for five years alone, when this time had elapsed and finally agreed (in 1596) with its brother to a new divisionary treaty.
The duchy of Saxe-Eisenach was taken by Johann Ernst as independent principality separated from Saxe-Coburg, who remained with Johann Casimir.
Thus, Saxe-Eisenach, for the first time in his history, had his own independent political unit became within the Holy Roman Empire.
During his first year of reign, Johann Ernst still live in Marsuhl because Eisenach, the new capital of his country, was inhabited and, only with the establishment of his official residence
the citizens began to moved there.
In 1598 Johann Ernst created for his duchy his own "Landesregierung" (Federal State Government) and a" Konsistorium".
In 1633 his brother, the duke Johann Casimir of Saxe-Coburg, died childless.
For this, Johann Ernst inherited Saxe-Coburg, and until his own death he governed both countries in a personal union, but maintains, however, his residence in Eisenach.
In Wiener Neustadt on 23 November 1591 Johann Ernst married firstly with Elisabeth of Mansfeld-Hinterort.
She died four days after giving birth to their only son:
In Rotenburg on 14 May 1598 Johann Ernst married secondly with Christine of Hesse-Kassel.
The marriage was happy, but remained childless.
With the death of Johann Ernst ended the older line of Saxe-Coburg-Eisenach.
His principality was divided (under the rules of the Ernestine line) between Saxe-Weimar and Saxe-Altenburg.
William Ernest, Duke of Saxe-Weimar
William Ernest, Duke of Saxe- Weimar( 19 October 1662 – 26 August 1728) was a duke of Saxe- Weimar.
Fredericka Elisabeth of Saxe-Eisenach
Fredericka Elisabeth of Saxe- Eisenach( 5 May 1669- 12 November 1730), was a German noblewoman member of the House of Wettin and by marriage Duchess of Saxe- Weissenfels.
Born in Altenkirchen, she was the seventh of eight children born from the marriage of John George I, Duke of Saxe- Eisenach and Johannetta, Countess of Sayn- Wittgenstein- Sayn- Altenkirchen.
From her seven older and younger siblings four survive adulthood: Eleonore Erdmuthe Luise( by her two marriages Margravine of Brandenburg- Ansbach and Electress of Saxony), Frederick August, Hereditary Prince of Saxe- Eisenach, John George II, Duke of Saxe- Eisenach and John William, Duke of Saxe- Eisenach.
Dorothea Maria of Saxe-Gotha-Altenburg
Dorothea Maria of Saxe- Gotha-Altenburg( 12 February 1654 in Gotha – 17 June 1682 in Gotha), was a German princess member of the House of Wettin in the Ernestine branch of Saxe- Gotha- Altenburg.
She was the twelfth child and fourth daughter of Ernest I, Duke of Saxe- Gotha by his wife Elisabeth Sophie, the only daughter of John Philip, Duke of Saxe- Altenburg.
William August, Duke of Saxe-Eisenach
Wilhelm August, Duke of Saxe- Eisenach( 30 November 1668 – 23 February 1671) was a duke of Saxe- Eisenach.
He was born at Eisenach, the youngest and only surviving son of Adolf Wilhelm, Duke of Saxe- Eisenach and Marie Elisabeth of Brunswick- Wolfenbüttel.
All his older brothers died before his father, and Wilhelm August, the fifth and youngest child, was born nine days after the death of Adolf Wilhelm( 21 November 1668) and succeeded him in the duchy of Saxe- Eisenach from the moment of his birth, under the guardianship of his uncle Johann Georg.
A sickly boy, he died at Eisenach when only two years old, and Eisenach was inherited by Johann Georg.
John George II, Duke of Saxe-Eisenach
Johann Georg II, Duke of Saxe- Eisenach( Friedewald, 24 July
1665 – Eisenach, 10 November 1698), was a duke of Saxe- Eisenach.
He was the second son of Johann Georg I, Duke of Saxe- Eisenach and Johannetta of Sayn- Wittgenstein.
The death of his older brother, Frederick August—who was killed in battle in 1684 — make him the new heir of the duchy of Saxe- Eisenach.
Two years later( 1686), Johann Georg succeeded his father when he died.
In Kirchheim unter Teck on 20 September 1688 Johann Georg married with Sophie Charlotte of Württemberg.
This union was childless.
When his cousin, the young Duke Johann Wilhelm of Saxe- Jena died( 1690) Johann Georg inherited a part of his duchy, because he was compelled to make a divisionary treaty with the Duke Wilhelm Ernst of Saxe- Weimar, his other cousin and brother- in- law of the late duke.
Johann Georg died suddenly of smallpox, and was succeeded by his brother, Johann Wilhelm.
Wilhelm Heinrich, Duke of Saxe-Eisenach
Wilhelm Heinrich, Duke of Saxe- Eisenach( 10 November 1691 – 26 July 1741), was a duke of Saxe- Eisenach.
He was born in Oranjewoud, the eldest and only surviving son of Johann Wilhelm, Duke of Saxe- Eisenach and his first wife Amalie of Nassau- Dietz.
Wilhelm Heinrich first married Albertine Juliane of Nassau- Idstein( daughter George August, Count of Nassau- Idstein) in Idstein on 15 February 1713.
This marriage was childless.
He married his second wife Anna Sophie Charlotte of Brandenburg- Schwedt in Berlin on 3 June 1723, just eight months after the death of Albertine Juliane.
The second marriage was also childless.
Wilhelm Heinrich acceded to the duchy of Saxe- Eisenach in 1729 upon the death of his father and was succeeded by his second cousin, duke Ernst August I of Saxe- Weimar.
The personal union between Eisenach and Weimar created by this succession was only nominal until 1809, when the two patrimonies were formally united.
He died in Eisenach.
Christine of Hesse-Kassel (1578–1658)
Christine of Hesse-Kassel (19 October 1578 – 19 August 1658) was a German noblewoman member of the House of Hesse and by marriage Duchess of Saxe-Eisenach and Saxe-Coburg.
Born in Kassel, she was the tenth of eleven children born from the marriage of William IV, Landgrave of Hesse-Kassel and his wife Duchess Sabine of Württemberg.
She was probably named after both her paternal grandmother and aunt (by marriage Duchess consort of Schleswig-Holstein-Gottorp).
John William III, Duke of Saxe-Eisenach
John William III, Duke of Saxe- Eisenach( 17 October 1666 – 14 January 1729), was a duke of Saxe- Eisenach, and came from the Ernestine line of the house of Wettin.

Question: Who is John Ernest, Duke Of Saxe-Eisenach's mother-in-law?
Answer: Duchess Sabine of Württemberg