The teen, whose name was not released, was a family friend of the royal family and had been living with them since he arrived in Sweden as a refugee in 2010, The Local.se reported.
He allegedly stole a key in April and sold the majority of the jewels for 9,000 kronor ($1,280) to two marijuana dealers. He also threw a tiara worth 350,000 kronor ($49,811) off a bridge. He planned to blame the thefts on the housekeeper.
The jewels belonged to Princess Christina, 68, the youngest sister of Sweden's King Carl XVI Gustaf. Her husband, Tord Magnuson, discovered the treasure was missing. Magnuson questioned the 19-year-old, who admitted to the thefts, officials said.
The royal family filed charges of aggravated theft against the youth but he missing jewels have yet to be recovered.