Kate, who turns 39 today, is believed to be spending the day with her family at their Norfolk home of Anmer Hall.
The Cambridges spent Christmas at the residence after the Queen decided to have a quiet festive period at Windsor Castle, rather than throw the traditional family gathering at Sandringham.
A message on the Cambridges’ Twitter page said: ‘Thank you for your kind wishes on The Duchess’ birthday.
‘Birthdays have been very different in recent months, and our thoughts continue to be with all those working on the front line at this hugely challenging time.’
The message was accompanied by a photograph of Kate wearing a face mask and waving, which was taken while she and William spent three days in December touring the country by royal train to thank key workers for their efforts during the coronavirus pandemic.
Birthday wishes were also sent to Kate by the Prince of Wales and Duchess of Cornwall.
The Clarence House Twitter account posted a photo of the duchess taken during a visit to Battersea Park in September, where she met mothers to learn how they were helping each other during the pandemic, alongside the message: ‘Happy Birthday to The Duchess of Cambridge!’
Buckingham Palace tweeted a birthday message along two photos of Kate, one of her becoming joint president of the Scout Association, of which the Queen is a patron, and another of her with the monarch as she gave a guided tour of the garden she created for Chelsea Flower Show,
Kate’s birthday celebrations are likely to be a private affair, due to lockdown restrictions, with William and their three children -Prince George, seven, Princess Charlotte, five, and two-year-old Prince Louis.
Throughout the pandemic, the Cambridges have adapted their public life, turning to video calls to carry out virtual engagements and then joining socially distanced face-to-face events when restrictions were lifted.
In November, the duchess said she was ‘humbled’ that more than half-a-million people had taken part in her landmark research on the issue of early years.
The study was the largest of its kind in the UK on perceptions of early childhood – which found only one in four people recognise the key importance of the first five years of a child’s life.
Catherine Elizabeth Middleton was born to Carole and Michael Middleton at the Royal Berkshire Hospital in Reading on January 9, 1982.
Amman in Jordan was home to Kate and her family for a few years in the mid 1980s, where she attended a nursery school from the age of three, before returning to Berkshire.
At the age of 13, she went to the exclusive, private Marlborough College in Wiltshire, where she part-boarded.
She graduated in 2005 with a 2:1 in history of art from St Andrews University, where she met and began dating William, whom she married at Westminster Abbey in 2011.
Kate – now an HRH and a future Queen consort – is patron of 19 charities and organisations, and has focused her charity work on helping children have the best possible start in life, particularly surrounding their mental health.
They say never judge a book by its cover but they also said a picture is worth a thousand words...