Empress of Japan wears face mask in carriage with Queen Camilla due to allergic reaction fears

King Charles, 75, and Queen Camilla, 76, greeted their guests on the Horse Guards Parade.

The two Heads of State warmly shook hands as did their wives, Camilla and EmpressMasako.

Prince William escorted the Emperor and Empress from their overnight hotel in London, arriving almost 10 minutes late in chauffeur-driven cars.

His wife, Princess Kate, returned briefly to the spotlight at Trooping the Colour on June 15 despite her cancer treatment.

However, she is not expected to take part in the visit this week.

At the end of the welcome ceremony today, there was a traditional carriage procession to Buckingham Palace where a private lunch was held.

The two Heads of State sat together in the lead coach, followed by Camilla and the Empress who has a chronic allergy to horse hair.

Therefore, Masako wore a white face mask as a precaution.

Missing from the State Visit is Princess Anne, who remains in hospital today after suffering minor head injuries and concussion.

A horse reportedly kicked the Princess Royal on her Gatcombe Park estate in Gloucestershire on Sunday.

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At midday, the King and Queen had an awkward wait at the Horse Guards Parade because the Emperor and Empress of Japan were delayed in traffic.

Their Majesties arrived on schedule just before noon and were greeted by Sir Kenneth Olisa, His Majesty's Lord-Lieutenant of Greater London.

Emperor Naruhito and Empress Masako were originally scheduled to arrive at 12.10pm.

Buckingham Palace aides confirmed the unexpected delay was due to traffic.