A 3,000-year-old quartzite head of Egyptian "Boy King" Tutankhamun was auctioned off for $6 million on Thursday at Christie's auction house in London despite protests from the Egyptian government.
Christie's sold the 28.5-centimeter relic for £4,746,250 ($5,970,000, 5,290,000 euros) at one of its most controversial auctions in years.
No information about the buyer was disclosed.
The famous pharaoh's finely-chiselled face -- its calm eyes and puffed lips emoting a sense of eternal peace -- came from the private Resandro Collection of ancient art that Christie's last auctioned off 2016 for £3 million.
But angry Egyptian officials wanted Thursday's sale halted and the treasure returned.
Christie's decision "contradicts international agreements and conventions," Egypt's foreign ministry said on Wednesday.
Egypt holds rights to the piece based on its current and previous laws, it added.
Former antiquities minister Zahi Hawass told AFP that the piece appears to have been "stolen" in the 1970s from the Karnak Temple complex just north of Luxor.
"We think it left Egypt after 1970 because in that time other artifacts were stolen from Karnak Temple," Hawass said.
Christie's countered that Egypt had never before expressed the same level of concern about an item whose existence has been "well known and exhibited publicly" for many years.
"The object is not, and has not been, the subject of an investigation," it said in a statement to AFP.
The auction house has also said that it carried out "extensive due diligence" to verify the provenance of the statue and had "gone beyond what is required to assure legal title."
It published a chronology of how the relic changed hands between European art dealers over the past 50 years.
Its oldest attribution from 1973-74 places it in the collection of Prince Wilhelm of Thurn and Taxi in modern-day Germany.
Yet that account was called into doubt by a report from the Live Science news site last month suggesting that Wilhelm never owned the piece.
Wilhelm was "not a very art-interested person," his niece Daria told the news site.
A journalist and art historian who knew Wilhelm told Live Science site that the prince had no arts collection at all.
Tutankhamun is thought to have become a pharaoh at the age of nine and to have died about 10 years later.
His rule would have probably passed without notice were it not for the 1922 discovery by Britain's Howard Carter of his nearly intact tomb.
