Marie Antoinette

Fourteen-year-old Madame Antoine (Kirsten Dunst) is the beautiful, charming, and naive archduchess of Austria, youngest of Empress Maria Theresa's (Marianne Faithfull) daughters. In 1770, the only one left unmarried among her sisters, she is sent by her mother to marry the Dauphin of France, the future Louis XVI of France (Jason Schwartzman), to seal an alliance between the two rival countries. Marie Antoinette travels to France, relinquishing all connections with her home country, including her pet Pug "Mops", and meets the King Louis XV of France (Rip Torn) and her future husband, Louis Auguste. The two arrive at the Palace of Versailles, which was built by the King's great-grand uncle. They are married at once, and are encouraged to produce an heir to the throne as soon as possible; but the next day it is reported to the king that "nothing happened" on the wedding night.
As time passes, Marie Antoinette finds life at the court of Versailles stifling. Her husband's courtiers disdain her as a foreigner, and blame her for not producing an heir, although the fault really lies with her husband, for the marriage remains unconsummated for an inordinate amount of time. The French court is rife with gossip, and Marie Antoinette consistently ruffles feathers by defying its ritualistic formality. Marie Antoinette also refuses to meet or speak with Jeanne BÃ©cu, Madame du Barry (Asia Argento), the mistress of Louis XV. Over the years, Maria Theresa continues to write to her daughter, giving advice on how to impress and seduce the Dauphin. Unfortunately, Marie's attempts to have sex with her husband fail and the marriage remains childless. Marie spends most of her time buying extravagant clothes and gambling. After a masquerade ball, Marie and Louis XVI return to find that the King has smallpox; he orders du Barry to leave Versailles, and soon dies. Louis XVI is crowned King of France, with Marie as Queen.
Marie Antoinette's brother, Joseph II, Holy Roman Emperor (Danny Huston) comes to visit, counseling her against her constant parties; advice that she finds easy to ignore. Joseph meets Louis XVI at the Royal Zoo and explains to him the "mechanics" of sexual intercourse in terms of "key-making", as one of the King's favorite hobbies is locksmithing. Thereafter, the King and Marie Antoinette have sex for the first time, and on December 18, 1778, Marie Antoinette gives birth to a daughter, Princess Marie ThÃ©rÃ¨se of France. As the baby princess grows up, Marie Antoinette spends much of her time at the Petit Trianon, a small chateau in the park of Versailles. It is also at this time that she begins an affair with Axel Fersen (Jamie Dornan). As France's financial crisis worsens, food shortages and riots increase. Marie Antoinette's image with her subjects has completely deteriorated by this point: her luxurious lifestyle and seeming indifference to the struggles of the masses earn her the title Madame DÃ©ficit.
As the queen matures, she focuses less on her social life and more on her family, and makes what she considers to be significant financial adjustments. A year after her mother's death on November 29, 1780, Marie Antoinette gives birth to a son, Louis Joseph, Dauphin of France on October 22, 1781. She also gives birth to another son, Louis XVII of France on March 27, 1785, and another daughter, Princess Sophie of France on July 9, 1786, who dies on June 19, 1787, a month before her first birthday. As the French Revolution erupts with the storming of the Bastille, the royal family resolves to stay in France, unlike many of the nobility. Rioting Parisians force the family to leave Versailles for Paris. The film ends with the royal family's transfer to Tuileries Palace. The last image is a shot of Marie Antoinette's bedroom, destroyed by angry rioters.

Question: When was her first son born?