The Sussexes may not go to the historic event, according to royal biographer Angela Levin, because of the perceived slight.
Within a few days, the couple is expected to respond to their invitation.
Despite this, key members of the Royal Family such as King Charles, Prince William, Kate Middleton and Sophie, Duchess of Edinburgh will almost certainly appear on the Buckingham Palace balcony.
Buckingham Palace is undoubtedly the most iconic of all the royal residencies, but what does it look like inside?
READ MORE: Kate and William broke rule at Easter and late Queen looked confused
Although Buckingham Palace offers a huge 829,000 square feet of living area, the late Queen never wanted it as her preferred royal abode.
At a projected cost of £369million, Buckingham Palace is currently undergoing substantial repairs and modernisation.
It has 775 rooms total, which includes 19 staterooms, 52 royal and guest beds, 92 offices, 78 bathrooms, and 188 staff bedrooms.
The palace also has a chapel, a post office, an indoor pool, a staff cafeteria, a doctor’s office, and a theatre.
The balcony, which is located at the front of the home and is used by the royals at important events like Trooping the Colour and royal weddings, is one of Buckingham Palace’s most recognisable features.
King Charles has been subtly enhancing the place with his own unique touches.
The 47-meter picture gallery was created by architect John Nash as part of George IV’s renovation of Buckingham Palace in the 1820s to display the former King’s art collection, but he did not live to see it finished.
An image of the yellow drawing room was previously posted on the official Royal Family Instagram account.
READ MORE: Expert claims ‘dominant’ Princess Charlotte ‘keeps an eye’ on Louis
Many of the late Queen’s official photos and Christmas programmes have happened in the lovely Regency Room.
The room contains tassel-trimmed sofas, a desk, and a traditional fireplace. It is decorated in green and gold.
The Grand Staircase, which leads to the State Rooms upstairs, is one of the first things guests notice when they enter the palace.
A striking first impression is created by the red carpet that runs the stairs and the historical portraits of the Royal Family that are hung on the walls.