WASHINGTON — It was a message that was perfectly timed, seeking to reassure a young Iranian monarch in crisis. And it came from the world's most prominent royal, Britain's Queen Elizabeth.

But it soon became clear there was no such message from London. It was a snafu, a garbled diplomatic note and a case of mistaken identity the Americans continued exploiting for their own purposes even after realizing their mistake.

According to "The Queen and the Coup," a documentary airing this month in Britain citing newly discovered U.S. documents, the comedy of errors may have played a key role in the 1953 CIA-British coup that toppled the democratic government of Iran.

The 1953 takeover, which restored Shah Mohammad Reza Pahlavi of Iran to power and has fueled distrust between the U.S. and Iran ever since, has inspired numerous books, documentaries and academic research. But nearly seven decades later, British historians have uncovered State Department documents in U.S. national archives that reveal a new twist in the run-up to the coup.

The key document comes from February 1953, five months before British and U.S. spies helped overthrow the parliamentary government led by Prime Minister Mohammad Mossadegh. The shah of Iran was teetering, and considering fleeing the country, which would effectively wreck the joint British-U.S. plot before it even began.

The document had never come to public attention until now, even though it had been declassified along with other documents in the U.S. archives, according to the documentary produced by Brave New Media for Britain's Channel 4.