Just four days before King Edward VII arrived in Ireland for a state visit, his Crown Jewels were stolen from Dublin Castle.

The 1907 theft angered the monarch, scandalised the Irish press and has remained one of the unsolved mysteries of modern times.

The star and badge of the Order of St Patrick, laden with rubies, emeralds and diamonds, were never recovered.

Now an historian has blamed the daring heist on Francis Shackleton, brother of the famous polar explorer Ernest, and revealed that his knowledge of gay activities within the Castle was one of the reasons he was never brought to justice.

In his position as Dublin Herald, Shackleton shared a house with the man entrusted with the security of the Jewels, Sir Arthur Vicars, the Ulster King of Arms.

Historian Sean J Murphy has examined the available evidence and is convinced that Shackleton’s implied threat to expose a gay sex ring at the heart of the British government in Ireland allowed him to escape prosecution.

“I have seen the records of Shackleton’s interviews and they are a masterpiece of control of his interrogators,” Mr Murphy told the Irish Independent.

“Shackleton is threatening to reveal all sorts of information if he is pressed too hard.”

Shackleton did not escape prison forever though; in 1913 he was convicted of fraud after defrauding a widow of her savings.

The Order of St Partick is an order of chivalry founded in 1783 by George III.

It still exists, though since Irish independence no new knights have been created. The last knight, the Duke of Gloucester, died in 1974.