Louisa Maria's father
By British School via Wikimedia Commons
William Henry's "love match" didn't prevent him from straying, which brings us to today's "princess": his illegitimate daughter Louisa Maria La Coast. William Henry had fallen for one of his Duchess's ladies-in-waiting, Lady Almeria Carpenter. After the birth of her daughter in 1782, Almeria stayed on as a permanent third wheel in the royal marriage, even traveling with the couple to fled to live on the continent for financial reasons--another downfall of George's brothers and sons.
Meanwhile, little Louisa Maria was raised on a dairy farm by her father's steward. When she was old enough, she ran off with Godfrey Bosville Macdonald, who later became the 3rd Baron Macdonald of Slate. The couple didn't marry under English law, instead they simply pledged themselves to each other, which was good enough in Scotland, where they were living. The first three of their 13 children were born, therefore, without being legitimate according to English law. When they finally married, they seem to have hidden this fact from the children. It is said that eldest son Alexander had lived in expectation of inheriting his father's title. He was dining at a neighbor's house when word reached the dinner party that Baron Macdonald had died. As he prepared to withdraw with haste, his cruel hostess ordered him to sit back down, saying, "You are not Lord Macdonald." With this rude awakening, he learned the secret of his birth and that his younger brother, born after his parents' legal marriage, was now the 4th Baron Macdonald.
Louisa Maria died in 1832.