The King rolled out a rather soggy red carpet today as senior royals welcomed the Sultan of Oman - described as one of the world's 'most discreet billionaires' - to Windsor Castle for a State Visit.

Amid full pomp and pageantry despite the rain, the Princess of Wales beamed in a green Sarah Burton for Alexander McQueen coat with a matching hat by Juliette Botterill and distinctive green earrings, alongside a dapper Prince William.

The King looked in good spirits, and equally smart in morning dress, with Queen Camilla resplendent in a red wool crepe dress and coat by Fiona Clare with a hat by Philip Treacy and a ruby and diamond flower brooch.

His Majesty took off his top hat to greet the Sultan, giving him a wide smile as he shook his hand following the Omani ruler's arrival.

Kate smiled and gave a deep curtsey as she also shook Sultan Haitham bin Tarik Al Said's hand in the royal line-up.

William met the Sultan at one of his private UK residences before escorting him to Windsor where the King, Queen and the princess, who had travelled down together from the castle a few minutes earlier, were waiting to meet him in the town centre.

In a change to the traditional arrangements, Kate did not accompany William to the Sultan's private residence. The planned adjustment was made because the Sultan is not being accompanied by his wife during his stay.

After the formal greetings they travelled back to the castle in a procession of carriages for a full ceremonial welcome in the castle quadrangle.

The Sultan joined the King in the Irish State Coach for a horse-drawn carriage procession through the streets of Windsor to the castle, ready to attend the ceremonial welcome in the quadrangle.

Charles was seen to pat down his hair as he sat in the carriage as the Household Cavalry readied their horses for the start of the short journey.

The Queen followed in the second carriage – the Scottish State Coach – accompanied by Oman's deputy prime minister for defence affairs Sayyid Shihab bin Tariq Al Said.

The Prince and Princess of Wales were in the third carriage – the Australian State Coach – with the deputy prime minister for economic affairs Sayyid Theyazin bin Haitham Al Said and secretary general of the diwan of the royal court Sayyid Loay bin Ghalib Al Said. 

Taking in Thames Street High Street, Park Street and the castle's Cambridge Gate – with the route lined by an impressive display of all three Armed Forces – the procession entered through the George IV Gateway into Windsor Castle.

The King then invited his guest to inspect a Guard of Honour before the group moved inside for a private lunch.

Following lunch, the royal party went to the castle's Green Drawing Room where a display of items from the historic Royal Collection highlighting the warmth of UK/Omani relations over the centuries had been set out for the guests to examine.

The King and Queen escorted the sultan, followed by the Prince and Princess of Wales and the Duke and Duchess of Edinburgh.

Charles showed off two of his own paintings to the Sultan - two landscape water colour paintings from his trip to Oman in 1995 - the first time he own artwork has been displayed as King.

Charles told the Sultan: 'These are two of my paintings.'

The Sultan nodded and said 'good'.

When the princess arrived at the King's paintings, she told guests: 'These are paintings by His Majesty. He is a very good water colourist himself.'

Other artefacts on display included an Abraham Parsons 1775 travel account of Muscat, tiara given by Oman to Queen Victoria for her 1838 Coronation, and 1647 gold medallion of Queen Elizabeth I given on 1982 State Visit.

In the evening, His Majesty, accompanied by the Queen and members of the Royal Family, will give a glittering State Banquet at Windsor Castle for the Sultan – the highlight of which will undoubtedly be the ladies' gowns and tiaras.

The King and His Majesty Sultan Haitham bin Tarik will deliver speeches at the beginning of the banquet.

The present Sultan acceded to the throne in 2020 following the death of his cousin, Sultan Qaboos bin Said, becoming the 15th ruler of the Al Bu Said dynasty which has ruled Oman since the mid-18th century.

He has also been called 'one of the most discreet billionaires alive'.

The Sultan is married with four children, although his wife is not accompanying him on this State Visit.

The ruling Omani family has enjoyed good relations with the British Royal Family and the Sultan has met the King and Queen on several occasions previously. Oman is considered one of Britain's oldest friends in Arabia.

One of the Sultan's main challenges is seen to be the need to oversee Oman's transition from over-reliance on oil revenues to a diversified economy.