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The Duchess of Cambridge is self-isolating today after coming into close contact with someone who has tested positive for Covid-19 - despite having both her jabs and testing negative twice in the past week.

Kensington Palace has not revealed where or when exactly the contact was, only saying it was 'last week', meaning it could have been when she visited Wimbledon on Friday or during England's historic win over Germany at Wembley on Tuesday night.

The Duchess arrived at the All England Club at around midday and was joined by Wimbledon chief executive Sally Bolton and former British tennis player Tim Henman on an outside court where they watched Andy Murray's brother Jamie play.

She was also pictured laughing and smiling as she prepped strawberry desserts at the All England Club before heading to the Royal Box where she seen speaking to a beaming Joe Wicks, leaving around 5pm. 

MailOnline understands that the Duchess was alerted about the contact with a Covid-infected person on Friday afternoon.

Kate's only other public engagement was on Tuesday when she went to Wembley Stadium with William and George to watch England beat Germany. 

A palace source said that the Duchess took lateral flow tests before her engagements at the Euros match and Wimbledon and both were negative.

In addition to this, the Duchess is tested twice weekly with lateral flow tests as part of the Royal Household testing regime.

'Last week The Duchess of Cambridge came into contact with someone who has subsequently tested positive for Covid-19', her spokesman said, adding: 'Her Royal Highness is not experiencing any symptoms, but is following all relevant government guidelines and is self-isolating at home'.

It is not known if the Duchess of Cambridge was alerted after being 'pinged' via the NHS app, a phone call from test and trace or if she or her team was contacted personally by the person who tested positive. 

It means that William is having to lead and celebrate the 73rd anniversary of the NHS today, alone. The couple were due to attend a service of thanksgiving at St Paul's Cathedral this morning before hosting an afternoon tea at Buckingham Palace. 

But the Duke of Cambridge is now flying solo.

The Duchess, who is self-isolating today, was joined by Wimbledon chief executive Sally Bolton and former British tennis player Tim Henman on Friday during a visit that may have forced her to quarantine at home

At one point the Duchess of Cambridge checked a mobile phone. It is not known if she was pinged via the NHS app. Later she prepped some strawberries to be eaten with cream

The Duchess of Cambridge chats with the beaming Body Coach Joe Wicks in the Royal Box at Centre Court on Friday afternoon

The Duke of Cambridge arrives for the NHS service of commemoration and thanksgiving to mark the 73rd birthday of the NHS at St Paul's Cathedral, London, without the Duchess of Cambridge

The Duchess headed to the All England Club's kitchen where she helped prepare the classic Wimbledon snack of strawberries and cream

 Kate's last public event was a visit to Wimbledon on Friday when she toured the SW19 sporting venue meeting staff in the museum, Centre Court kitchen and sitting with former tennis star Tim Henman to watch Jamie Murray play in the doubles.

The duchess is patron of the All England Lawn Tennis Club and a keen tennis fan but is now likely to miss the men's and Women's final at the weekend.

Her only other public engagement was at Wembley, but it is not known if she attended any other events last week. 

William contracted Covid last spring and was able to carry on with telephone and online engagements while he was treated by royal doctors but was reportedly hit 'pretty hard' by the virus and at one stage struggled to breathe.

The Prince of Wales also caught the virus during the same period but had milder symptoms although he did lose his sense of smell and taste for a period.

William, Kate and George after England beat Germany, pictured in front of Culture Secretary Oliver Dowden with the Beckhams and Ed Sheeran to their right (out of picture)

The Duke of Cambridge will celebrate the 73rd anniversary of the NHS at a service of thanksgiving before hosting a tea at Buckingham Palace - without his wife. 

William was due to attend both events with Kate, but it was announced today the Duchess will miss the engagements after coming into contact with someone who has tested positive for Covid-19.

The Duchess does not have any symptoms but is following government advice and self-isolating at home.

The service at St Paul's Cathedral will celebrate the NHS's contribution to the country during Covid-19, reflecting on the work and achievement of health staff, volunteers and carers.

William will join guests including leading figures in the NHS pandemic response, several hundred members of frontline staff, and patients.

Later he will host the NHS Big Tea in the grounds of Buckingham Palace to pay tribute to the work of NHS staff who have gone above and beyond in tackling the pandemic.