Margareta Slots, née Cabiljau, had a brief affair with King Gustav II Adolf in the mid-1610s. They had a son together, whom the king acknowledged as his. The son was named Gustaf, and later ennobled as Gustaf Gustafsson af Wasaborg.

Margareta Slots was the daughter of Maria van Leest and Abraham Cabiljau, a businessman and town mayor from the Netherlands. Her parents were part of the relatively sizable group of entrepreneurs who immigrated to Sweden during the seventeenth century and successfully established themselves there.

As her parents arrived in Sweden in 1607, and Margareta Slots’ relationship with King Gustav II Adolf occurred in 1615, the very latest she could have been born was in 1600. Some sources state that she was born in 1595. In any case, by 1615 she had married her first husband, Andries Serssander, who was a Dutch fortifications officer. However, he died at Pskov that same year, when Swedish troops led by Henrik Horn and King Gustav II Adolf were laying siege to the town. It was presumably there, in Pskov, that Margareta Slots began her relationship with the king. No information survives on how they met, or how long their relationship lasted. It seems to have been a brief fling.

On 24 May 1616 Margareta Slots gave birth to her son Gustaf. King Gustav II Adolf acknowledged the boy as his. Margareta Slots was awarded several farms in Kalmar which she then sold in order to pay off her husband’s debts. She also received a maintenance fee from the royal court so that she and her son had an income to live off.

At some point between the death of her first husband and 1619, when Margareta Slots married Jacob Trellow, a gunpowder maker, she had married Arendt Slots, also a Dutchman. Nothing is known of when they met, how the marriage was arranged or when Slots died. A little more information exists surrounding Margareta Slots' third marriage, as she and her new husband were awarded the Benhammar (now Stora Benhamra) estate in Vada parish in Vallentuna as a royal donation.

In 1625 Margareta Slots was charged with manslaughter of a low-ranking official. The official had been killed by her employees in her presence, and she was believed to have sanctioned the act. The official had irritated Margareta Slots by demanding payments from her disobedient peasants as they had failed to perform their obligations regarding road maintenance. She admitted the charge and the case was referred to King Gustav II Adolf. The outcome remains unclear. Margareta Slots appears to have spent the rest of her life at Stora Benhamra farm.

Her son Gustaf began studying at Uppsala University in 1626. After the death of King Gustav II Adolf in 1632, Chancellor Axel Oxenstierna became the boy’s guardian. In 1637 Gustaf was ennobled and was made both baron and count in 1646. He was also appointed privy councillor that year but Queen Kristina did not have a lot of faith in him. He moved to Germany in 1652 and died the following year. He had a successful career which must largely be attributed to the fact that he was the son of King Gustav II Adolf.

Margareta Slots' personal history is only known due to the fact that she had a son with King Gustav II Adolf. Her story is an example of the pragmatic approach to – and to some degree tolerant view of – extramarital affairs in the upper social classes at the time.

Margareta Slots died in 1669. Her grave lies in Vada church in Uppland.