The sculpture of Queen Nefertiti stands in a Berlin museum
Newly published documents show how a German archaeologist used trickery to smuggle home a fabulous sculpture of the Egyptian queen, Nefertiti.
The archaeologist, Ludwig Borchardt, listed the bust of Queen Nefertiti among his finds in Egypt in 1913.
But he described it as a worthless piece of gypsum and hid it in a box.
It is now regarded as a supreme artefact of the Pharaonic era and attracts half a million visitors per year to Berlin's Egyptian Museum.
The BBC correspondent in Cairo, Christian Fraser, says the document that has ignited this latest row was discovered in the German Oriental Institute.
It is the account of a meeting between Ludwig Borchardt and an inspector of antiquities to discuss an inventory of the archaeologist's discoveries.
There was an agreement for Germany and Egypt to divide the spoils equally.
But the bust of Queen Nefertiti - who reigned as wife of the Sun King Akhenaten more than 3,000 years ago - was so exquisite that Mr Borchardt determined to keep it "for Germany", the account says.
The queen was tightly wrapped, placed in a box in a poorly-lit chamber and kept hidden. The photograph of her that Mr Borchardt handed over was deliberately unflattering.
He described Nefertiti as being made of gypsum, which is almost worthless, whereas in fact her regal features were painted on limestone.
The notes from Mr Borchardt's diary reveal that he knew the sculpture's real value.
"It is indescribable," he said. "You have to see it with your own eyes."
Egypt's Supreme Council of Antiquities confirmed it had been made aware of the document.
The evidence of this deception could well strengthen Cairo's bid to retrieve their ancient queen, our correspondent says.