In the Autumn of 1647 Mary suffered a miscarriage, after which she couldn't conceive for several years.
In early 1650, she was pregnant again.
In late October-early November, when the princess's pregnancy was coming to an end, her husband fell ill with smallpox and died on 6 November, just after his attempt to capture Amsterdam from his political opponents; two days before his death, on the day of her nineteenth birthday, Mary gave birth to a son, William.
The newborn prince's cradle was draped with black cloth as a sign of sorrow for his father.
Since the titles of the stadtholder of the Netherlands and the Prince of Orange were not inheritable, little William didn't receive them immediately after birth.

Soon after the birth of her son, Mary had several conflicts with her mother-in-law.
She planned to name her son Charles in honor of her executed father, but Amalia insisted that the boy be named William, which was a better choice: the first ruler of the United Provinces of the Netherlands was William I of Orange and in addition, the boy's late father also wanted to name his son William.
Having won the battle for the name of her grandson, Amalia now wanted to become her legal guardian, referring to the fact that Mary is too young.
On 13 August 1651, the Hoge Raad van Holland en Zeeland (Supreme Court) ruled that guardianship would be shared between Mary, her mother-in-law and Frederick William, Elector of Brandenburg (whose wife, Louise Henriette was William II's eldest sister); the Elector was chosen because he could act as a neutral party mediating between the two women, but also because as a possible heir he was interested in protecting the Orange family fortune, which Amalia feared Mary would squander.

In general, Mary was not popular in the Netherlands, which were more sympathetic to Oliver Cromwell; the princess herself, because of such preferences of the Dutch, refused to hire them to serve her son.
In January 1650, Mary, along with her brother James and aunt Elizabeth, planned to modestly celebrate the first anniversary of her father's death, but the Dutch government considered even modest events offensive to the English government.
A little later, when envoys from the English parliament were received by the States General, Mary retired to her widow's seat in Breda, but the influence of her party didn't allow the British to conclude an alliance with the Netherlands.
After Mary secretly received her brother Charles II in 1651 (who considered himself the legitimate King of England), the Dutch government forbade her to accept any of her relatives.
The household of Mary and her aunt was called a "nest of vipers", weaving conspiracies against the Netherlands, England and Cromwell in particular.

In 1652, the mood in the Netherlands changed due to the outbreak of war with England.
Mary's son was officially elected as the stadtholder of Zealand and several northern provinces, but Witte de With, the leader of the republic, prevented from William III being elected in Holland; in addition, when concluding a peace treaty, Cromwell insisted on the adoption of the Act of Seclusion, which prohibited Holland from appointing members of the Orange dynasty to the post of stadtholder.
Another requirement of Cromwell was the expulsion of all enemies of the Commonwealth from Holland.
Mary made an official protest, but it was not taken into account, despite the fact that the country was threatened by civil war; the peace treaty was signed on 27 May 1654.

Mary's worries about the position of her son affected her health.
To cut her own expenses in the interests of her brothers, she announced her intention to abandon two of the four palaces at her disposal.
In July 1654, she went to a water resort, where she spent a few weeks, and then came to visit her brother Charles in Cologne, where his court was located.
She returned to the Netherlands in October, but in July 1655 she again went to Charles in Cologne, visited the fair in Frankfurt incognito and returned home on 15 November.
In January 1656, Mary went to Paris, where her mother and yo
In the Autumn of 1647 Mary suffered a miscarriage, after which she couldn't conceive for several years. In early 1650, she was pregnant again. In late October-early November, when the princess's pregnancy was coming to an end, her husband fell ill with smallpox and died on 6 November, just after his attempt to capture Amsterdam from his political opponents; two days before his death, on the day of her nineteenth birthday, Mary gave birth to a son, William. The newborn prince's cradle was draped with black cloth as a sign of sorrow for his father. Since the titles of the stadtholder of the Netherlands and the Prince of Orange were not inheritable, little William didn't receive them immediately after birth.
Soon after the birth of her son, Mary had several conflicts with her mother-in-law. She planned to name her son Charles in honor of her executed father, but Amalia insisted that the boy be named William, which was a better choice: the first ruler of the United Provinces of the Netherlands was William I of Orange and in addition, the boy's late father also wanted to name his son William. Having won the battle for the name of her grandson, Amalia now wanted to become her legal guardian, referring to the fact that Mary is too young. On 13 August 1651, the Hoge Raad van Holland en Zeeland (Supreme Court) ruled that guardianship would be shared between Mary, her mother-in-law and Frederick William, Elector of Brandenburg (whose wife, Louise Henriette was William II's eldest sister); the Elector was chosen because he could act as a neutral party mediating between the two women, but also because as a possible heir he was interested in protecting the Orange family fortune, which Amalia feared Mary would squander.
In general, Mary was not popular in the Netherlands, which were more sympathetic to Oliver Cromwell; the princess herself, because of such preferences of the Dutch, refused to hire them to serve her son. In January 1650, Mary, along with her brother James and aunt Elizabeth, planned to modestly celebrate the first anniversary of her father's death, but the Dutch government considered even modest events offensive to the English government. A little later, when envoys from the English parliament were received by the States General, Mary retired to her widow's seat in Breda, but the influence of her party didn't allow the British to conclude an alliance with the Netherlands. After Mary secretly received her brother Charles II in 1651 (who considered himself the legitimate King of England), the Dutch government forbade her to accept any of her relatives. The household of Mary and her aunt was called a "nest of vipers", weaving conspiracies against the Netherlands, England and Cromwell in particular.
In 1652, the mood in the Netherlands changed due to the outbreak of war with England. Mary's son was officially elected as the stadtholder of Zealand and several northern provinces, but Witte de With, the leader of the republic, prevented from William III being elected in Holland; in addition, when concluding a peace treaty, Cromwell insisted on the adoption of the Act of Seclusion, which prohibited Holland from appointing members of the Orange dynasty to the post of stadtholder. Another requirement of Cromwell was the expulsion of all enemies of the Commonwealth from Holland. Mary made an official protest, but it was not taken into account, despite the fact that the country was threatened by civil war; the peace treaty was signed on 27 May 1654.
Mary's worries about the position of her son affected her health. To cut her own expenses in the interests of her brothers, she announced her intention to abandon two of the four palaces at her disposal. In July 1654, she went to a water resort, where she spent a few weeks, and then came to visit her brother Charles in Cologne, where his court was located. She returned to the Netherlands in October, but in July 1655 she again went to Charles in Cologne, visited the fair in Frankfurt incognito and returned home on 15 November. In January 1656, Mary went to Paris, where her mother and yo
Mary, Princess Royal and Princess of Orange