QUEEN ELIZABETH TO MISS OPENING OF PARLIAMENT

There are a few dates on a British monarch’s royal calendar that are circled in red, and the state opening of Parliament is one of them.

But on Monday night, less than 24 hours before the big event, Buckingham Palace announced that Queen Elizabeth II would not be attending because of health issues.

“The queen continues to experience episodic mobility problems and in consultation with her doctors has reluctantly decided that she will not attend the State Opening of Parliament tomorrow,” the palace said in a statement.

During the 96-year-old queen’s 70-year reign, she has only missed the event twice: in 1959 and 1963, when she was pregnant with sons Andrew and Edward. On those occasions, her duties were carried out by the Lord Chancellor.

This time, in her stead, Prince Charles will be the first heir to the throne in modern history to star at the main ceremonial event of the parliamentary year.

This will also be the first time Prince William, second in line to the throne, will attend.

Charles, 73, has stood in for his mother at a number of big events in recent months. And he has sat beside her at the opening of Parliament before. But this will be his most high-profile solo act yet — and might offer a glimpse of what a Charles monarchy might look like.

The palace said: “At Her Majesty’s request, and with the agreement of the relevant authorities, The Prince of Wales will read The Queen’s speech on Her Majesty’s behalf.”

The remarks are actually not the queen’s but written by the government, laying out its legislative agenda for the year.

The state opening of Parliament’s customs include a lawmaker being taken hostage, someone named Black Rod having a door slammed in her face three times, and a bejeweled crown arriving at the Palace of Westminster separate from the monarch, with its own escort.

As strange as this theatrical production can seem to outsiders, it’s also an important part of how this country is run.

Robert Hardman, author of “Queen of Our Times,” said that the queen not attending the state opening of Parliament was a “significant moment” in the transition of power from the queen to Charles.

“It goes to the heart of what a constitutional monarchy does — it’s the queen in Parliament,” he said.