Two West Norfolk charity fund raisers attended a Downing Street reception, hosted by Samantha Cameron, for Action for ME.
The Prime Minister's wife was able to meet many of the guests gathered in the State Rooms at the prestigious event.
ME – or Myalgic Encephalomyelitiis – is an illness close to Mrs Cameron's heart as she has known people affected by it.
The event was held to say a very special thank you to many of the charity's supporters, many of whom have helped the charity over many years. They included Helen Buckenham, from Dersingham and her sister Liz Smith, from Mundesley, who have raised almost £30,000 through online auctions.
Mrs Buckenham, 61, who has been an ME sufferer since 1991, said: 'Liz and I were asked if we'd be the face of the fundraisers, to represent them.
'It was all very informal. Mrs Cameron came in and said: 'Hi, I'm Sam.
'She's a very quiet, quite demure lady. She seemed to be very understanding of ME.'
Action for ME chief executive Sonya Chowdhury said: 'This was a fantastic opportunity for us to say thank you to some long-standing friends and hello to some new ones. When Samantha offered to host the event, we were absolutely thrilled.
'There can be few places in the world as iconic as Number 10 and we were delighted to be able to celebrate past successes, highlight the much that still needs to be done and share some of our exciting plans for the future at such a high-profile venue.
'Numbers had to be limited, but we were also able to also invite some of the eminent researchers and experts in the field of ME who we are funding to this very special event.
'Bringing people together and working collaboratively to achieve joint aims is a major part of our strategy going forward.
'It is a really exciting time for ME research with new findings emerging and the recent launch of the UK CFS/ME Research Collaborative, bringing real hope of attracting serious investment and new young researchers into the field.
Among those attending were yachtswoman turned internationally best-selling author Clare Francis, who is president of Action for ME, and the charity's ambassadors, leading businessman Robert Cathery, a long-term supporter of the charity, and six times world champion and double Olympian Anna Hemmings.
Comments: Our rules
We want our comments to be a lively and valuable part of our community - a place where readers can debate and engage with the most important local issues. The ability to comment on our stories is a privilege, not a right, however, and that privilege may be withdrawn if it is abused or misused.
Please report any comments that break our rules.
Read the rules here