The Queen will celebrate her 94th birthday on April 21.
While the Palace is expected to mark the occasion on social media, all family-related affairs, including telephone and video calls with family members, are to be kept private, the source added.
The announcement follows earlier confirmation by Buckingham Palace that the traditional parade held annually in mid-June to mark the Queen’s official birthday –– known as Trooping the Colour –– will not go ahead.
The parade gives the Queen, who is head of the United Kingdom’s armed forces, a chance to review her army. It traditionally moves from Buckingham Palace down the Mall to Horse Guard's Parade, with members of the royal family traveling on horseback or carriage.
By the numbers: Last year, more than 200 horses, 400 musicians and 1,400 officers took part in the parade.
According to the royal source, there are currently no plans in place for an alternative marking of the Queen’s official birthday.