Brookline — Like many foreigners before and after him, Mr. Songkla chose to rent an apartment in Brookline because it was near the university where he was studying, and left shortly after receiving his degree.

But Mr. Songkla, known in his own country as the Duke of Songkla, also happened to be a prince visiting from Thailand, then called Siam. And the family he brought to Brookline eventually included two future kings, one of whom still rules his country today.

Now, more than eight decades after the family of King Rama IX left Brookline for their homeland, a Thai historian has erected a plaque to mark the early roots of one of the world’s longest-serving monarchs — and a little-known chapter of Brookline history.

“I want to preserve Thai history in Massachusetts,” said Cholthanee Koerojna, founder of the King of Thailand Birthplace Foundation. “I think this will be very good for historic preservation.”

After nearly a decade of research into the royal family’s brief time in Massachusetts, Koerojna is working to install eight plaques, include the one installed in Brookline last weekend, across the commonwealth, from Martha’s Vineyard to Harvard Square. But the Brookline plaque, fixed to front of a Longwood Avenue apartment building, is different, marking the home where they lived, raised their children and entertained Thai students for almost two years.