Kate Middleton breaks cover as she heads to biggest royal duty since cancer treatment

The Princess of Wales is taking part in her biggest and most significant royal event since she finished cancer treatment by joining Prince William to welcome the Emir of Qatar and his wife at the start of their state visit to the UK

The Princess of Wales has been spotted as she makes her way to her biggest appearance yet since her cancer treatment ended - taking part in the Qatar state visit to the UK.

Kate, 42, who has recently finished treatment following her cancer diagnosis earlier this year, was seen with Prince William as they headed to London to welcome Sheikh Tamim bin Hamad Al Thani and the first of his three wives, Sheikha Jawaher at their private residence. The royals posed for traditional welcome pictures before William and Kate accompany the guests to nearby Horse Guards Parade in Whitehall where the King and senior members of the Government will be waiting and a ceremonial welcome will be staged.

But despite Kate being back for the ceremonial welcome, Queen Camilla will be missing after suffering significantly diminished reserves of energy following her chest infection. Doctors have urged Camilla, 77, to take time to rest and recover fully because of the lingering effects of the illness, which she contracted a month ago following her long-haul trip to Australia and Samoa.

Afterward the ceremonial welcome, the royal party and their guests will take part in a carriage procession along The Mall to Buckingham Palace ahead of lunch, where Camilla will join the King, William, Kate and the other guests. After lunch, visiting heads of state traditionally view a small exhibition of items associated with their country’s relationship with the UK and Kate will be among the royal party joining the Emir and his wife in the palace's picture gallery for the event.

However, Kate will not attend the state banquet hosted by the King in the palace's ballroom that evening, although William and Camilla will be there. The princess announced in September the completion of her chemotherapy treatment in a deeply personal video with her family and said her focus was "doing what I can to stay cancer free".

The princess had been receiving treatment for an undisclosed form of cancer since late February, with the King beginning his cancer care earlier that month following his cancer diagnosis after treatment for an enlarged prostate. She has made a few official appearances, joining senior members of the Royal Family for the Remembrance Sunday service at the Cenotaph and travelling with the Prince of Wales to Merseyside to meet the bereaved families of the Southport stabbings.

William previously he was looking forward to getting back to royal duties with his wife by his side, after a 'brutal' year where the princess and his father the King were both diagnosed with cancer. In a wide ranging interview, William said they both wanted to evolve their roles with a focus on "helping people".

A royal source said: "The Princess is feeling positive about the future and very much looking forward to representing the royal family at the state visit and beyond. Her work has always been a great tonic to her as she continues to concentrate on her recovery moving forward to the end of the year and beyond."

Kate has a busy week and will be hosting her annual Christmas carol service at Westminster Abbey on Friday, when she is expected to be joined by her children and husband for the event. Later this afternoon, the Emir will travel to the Palace of Westminster and address gathered parliamentarians and other invited guests in the Royal Robing Room, before joining a reception with MPs and peers. William will also host the Emir at his official London home Kensington Palace.

Sheikh Tamim, 44, was educated in Britain, attending public schools Sherborne and Harrow, before graduating from Sandhurst military academy. He set up Qatar Sports Investments in 2005, which owns the French football team Paris Saint-Germain.

On Wednesday, the final day of the two-day visit, the Emir will visit Sandhurst before travelling to Buckingham Palace to bid farewell formally to the King and Queen. Sheikh Tamim will also travel to Downing Street for bilateral talks with Keir Starmer.