The Queen sat at her desk in Windsor Castle's White Drawing Room as she addressed the nation on coronavirus Covid-19.
She wore a green dress with a pearl necklace as she praised the NHS, thanked key workers and expressed her sympathy at people suffering during this difficult time.
She teamed the dress with a stunning diamond and turquoise brooch, which used to belong to Queen Mary.
It features a large turquoise stone surrounded by diamonds.
The Queen's grandmother Queen Mary was given the piece on her wedding day, and left it to the now-monarch when she died in 1953.
She first wore it publicly in 2014 and has worn it a number of times since.
She last wore the piece in August to attend a craft sale at a church near Balmoral Castle.
She also wore it in May when she visited the British Airways headquarters at Heathrow to mark the company's 100th birthday.
Tonight's speech was only the fifth time the Queen has addressed the nation in this way.
It came just hours after Britain’s coronavirus death toll rose 621 in a day to 4,934 - including 29 patients with no underlying health conditions.
Drawing on her own experience as a child before assuming the role of mother to the nation, the monarch said: “It reminds me of the very first broadcast I made, in 1940, helped by my sister.
“We, as children, spoke from here at Windsor to children who had been evacuated from their homes and sent away for their own safety.
“Today, once again, many will feel a painful sense of separation from their loved ones.
“But now, as then, we know, deep down, that it is the right thing to do.”
Royal sources say the logistics and planning have been particularly difficult due to the nationwide lockdown, and fears over the risks to the Queen’s health after she entered isolation on the advice of the Government.
Windsor Castle’s White Drawing Room is said to have been chosen as a location for filming as it would allow a safe distance to be kept between the monarch and her camera operator.
The lone cameraman, meanwhile, was dressed from head to toe in the same type of protective equipment which doctors and nurses have been wearing to treat infected patients.
A royal source said: “The Queen will demonstrate, as she has done on so many occasions, why she is one of our greatest monarchs in history.
“It was never in doubt that she would address the nation, even in the face of such an invisible invader that could even breach Windsor Castle walls.
“Her words will echo those of her father George VI during the Second World War, bringing the country together in a moment of crisis.
“Now her words will fill the houses of millions of homes around the country and echo around the world to the Commonwealth’s two and a half billion citizens as we join forces to defeat this awful disease.”
