The monarch, 93, recorded the address at Windsor Castle, where she has been staying since mid-March with husband Prince Philip as the royal family began self-isolating and social distancing.
The Queen had previously agreed with the U.K. government to record a TV address, but she had been waiting for the right time. It is set to air on Sunday at 3 p.m. ET.
“Everyone has had some time to adjust to the new ways of living and working and it felt appropriate now to thank people and acknowledge the difficulties that many people are facing,” a royal source tells PEOPLE.
The Queen has only made a few similar addresses to the nation and the wider world during her 68-year reign (though she does record a Christmas message every year). Her past televised speeches occurred most famously on the eve of the funeral of Princess Diana in 1997, at her Diamond Jubilee in 2012, upon the death of her mother, the Queen Mother in 2002, and during the Gulf War in 1991.
The monarch is believed to be in good health and continuing her work, such as receiving her official paperwork and documents in her famous “red boxes,” behind the scenes. She is also continuing to hold her weekly audience with Prime Minister Johnson, although they are now taking place by phone.
When she relocated to Windsor, 30 miles west of London, the Queen issued a short written statement expressing solidarity with the country as its citizens went through the difficult times and upheaval that has come with the virus.
“As Philip and I arrive at Windsor today, we know that many individuals and families across the United Kingdom, and around the world, are entering a period of great concern and uncertainty,” she said.
“We are all being advised to change our normal routines and regular patterns of life for the greater good of the communities we live in and, in particular, to protect the most vulnerable within them. At times such as these, I am reminded that our nation’s history has been forged by people and communities coming together to work as one, concentrating our combined efforts with a focus on the common goal.”
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“We are enormously thankful for the expertise and commitment of our scientists, medical practitioners and emergency and public services; but now more than any time in our recent past, we all have a vitally important part to play as individuals – today and in the coming days, weeks and months.”