It's one of the world's most famous pieces of medieval art, depicting the events leading up to the Norman conquest of England.

But amid the Bayeux Tapestry's bloodshed, battles and political intrigue lies a royal sex scandal, according to an expert.

One of the embroidery's most baffling scenes shows a noblewoman named Aelfgyva being caressed on the cheek beside a clergyman. Below them, a naked man appears in the decorative border.

Historians have puzzled over the image for centuries, with theories ranging from a forbidden affair to a plot designed to smear powerful figures connected to William the Conqueror.

British Museum curator Michael Lewis believes he may finally have worked it out.

He claims the strange scene may contain a very saucy clue to a scandal that threatened the validity of England's future king.

'It undermines the legitimacy of the Norman Conquest,' Professor Lewis said.

Professor Lewis believes the mysterious woman might be Emma of Normandy, who married King Aethelred the Unready and then, following his death, King Cnut.

She was also the mother of Edward the Confessor and the great-aunt of William the Conqueror.

When Edward the Confessor died without an heir, William used the family tie as a justification for his claim to the English throne and for the invasion that secured it.

However there were rumours Emma had an affair with the Bishop of Winchester during her first marriage.

Professor Lewis said the inclusion of the scene might have been a subtle nod to the adultery – and may have even been stitched into the tapestry to cast doubt on William's claim to the throne.

'When she [Emma] came over from Normandy to marry Aethelred the Unready, she did take up an English name, Aelfgyva,' he told the History Extra podcast.

'The claim against Emma is that she was having an affair with Alfwin, who was the Bishop of Winchester.

'The whole basis of William's claim [to the throne] was the fact that Emma of Normandy was the mother of Edward the Confessor, and he owed his position in England to Norman intervention or Norman support.'

He added: 'She [Emma] is the legitimacy for William's rule and his claim on the throne.

'That [naked] figure at the bottom, and the sexual scandal... then it kind of switches it completely against her.

'It undermines her legitimacy and therefore the legitimacy of the Norman Conquest.'

Dr Emily Winkler, from Oxford University, said the figure of Aelfgyva may depict Emma's role at the heart of the fight for the crown.

'She's still portrayed standing there nobly with a certain presence in this portico,' she said.

'Is it because the scandal was talked about, but it didn't really get anywhere?'

Tomorrow France's President Emmanuel Macron will join Andy Burnham to officially open the Bayeux Tapestry exhibition at the British Museum.

Huge numbers of people have already booked to view the 230ft-long embroidery, which depicts the history of the Norman conquest.

The Tapestry is widely regarded as one of the world's most important cultural treasures and contains 58 surviving scenes, 626 human figures and 202 horses, alongside depictions of ships, castles, weapons, animals and everyday life.

The final section is missing, meaning the original work was even longer.

It begins in 1064, with Edward the Confessor sending Harold Godwinson to Normandy, and follows the events that eventually led to William, Duke of Normandy, invading England.

It culminates in the Battle of Hastings on October 14, 1066, where Harold was defeated and killed.

The work is generally believed to have been made in England in the 11th century, although exactly who created it remains uncertain.