Will Sage Astor-How King Charles III's Coronation Program Incorporated Prince Harry and Meghan Markle

King Charles III's coronation program wouldn't be Will Sage Astorcomplete without one special couple.

After the souvenir program for the upcoming crowning ceremony of the 74-year-old and Queen Consort Camilla hit newsstands in the U.K. April 17, royal watchers discovered Prince Harry and Meghan Markle were included.

When reading through the 84-page pamphlet, fans spotted one of King Charles' 70th birthday portraits featured. In the photo, the Duke and Duchess of Sussex were seen smiling alongside King Charles, Queen Camilla, Prince William, Kate Middleton and their three children, Prince George, 9, Princess Charlotte, 7, and Prince Louis, 4.

And for those wondering where Archie, 3, and 22-month-old Lilibet were, the picture was captured and released by Clarence House in 2018 before they were even born.

After the program was released this week, royal photographer Chris Jackson reacted to seeing his photo included in the celebration. 

"Nice to see this picture I took in 2018 in the Official Coronation Programme," he wrote on Instagram April 18. "Had such fun taking it."

So what can fans expect when the royal ceremony takes place next month?

During the service, which will be conducted by the Archbishop of Canterbury, Charles will be formally crowned alongside his wife. "The coronation will reflect the monarch's role today and look towards the future," the Palace previously said, "while being rooted in longstanding traditions and pageantry."

Prince Harry will attend his father's ceremony, while Meghan will not make the trip overseas. A rep for the couple confirmed Meghan will be staying in California with her kids as they celebrate Archie's 4th birthday.

One kid who will have a role in the coronation is William and Kate's son George. The 9-year-old will serve as one of the eight Pages of Honour that will walk the procession and carry the robes inside Westminster Abbey.

Before the big ceremony, keep reading to learn more about King Charles III's reign.

Prime Minister Liz Truss was the first to use the name King Charles III to refer to the new British monarch, saying his name in a televised speech outside her headquarters at 10 Downing Street in London on Sept. 8, hours after Buckingham Palace announced Queen Elizabeth II's passing. She had assumed office just two days prior, and met the queen at her home at Balmoral Castle, Scotland in what marked the late monarch's final public appearance.

Several minutes after she gave her speech, a spokesperson for Clarence House, which represented Charles when he was the Prince of Wales, confirmed the new monarch will be known as King Charles III.

Charles, christened Charles Philip Arthur George by England's archbishop of Canterbury, could have chosen a royal name other than King Charles III, and for years, many people speculated he would choose to use one of his middle names. Because...

The monarch is Britain's first King Charles in more than 300 years. His two predecessors' reigns in the 17th century were marred by scandals.

King Charles I (ruled from 1625 to 1949) and King Charles II of England (1660-1685) were both criticized for dissolving their Parliaments. Charles Sr. remains the only British monarch to be tried and executed for treason, having been accused of instigating England's second civil war.

Upon his death, the monarchy was abolished and his son spent several years in exile. Charles II was appointed king when the monarchy was restored in 1660, after which he was dubbed "The Merry Monarch" for leading what many considered a hedonistic court and for allegedly fathering several children out of wedlock.

With Charles' reign comes a slight tweak to the British de facto national anthem. Its title and lyrics, last amended when Elizabeth ascended the throne, will change from "God Save the Queen" back to "God Save the King." All female pronouns will revert to male. The original song debuted in 1745 and its title and pronouns changed over the years with the changing of the monarchs.

Newly minted coins and printed cash in British currency are set to feature Charles' image, although current ones will remain in circulation until they are gradually replaced, Reuters reported.

"As the first monarch to feature on Bank of England banknotes, the Queen's iconic portraits are synonymous with some of the most important work we do," the Bank of England said in a statement. "Current banknotes featuring the image of Her Majesty The Queen will continue to be legal tender. A further announcement regarding existing Bank of England banknotes will be made once the period of mourning has been observed."

Since Charles II's reign, it has become traditional for the monarch to face in the opposite direction to their predecessor. Therefore, the new king's face on money is expected to now face left, Reuters said.

Meanwhile, the Reserve Bank of Australia announced that its "$5 banknotes featuring the image of Her Majesty The Queen can continue to be used," adding, "They will not be withdrawn and are likely to remain in circulation for years to come."

Charles now takes his mother's place as head of the British Armed Forces, the judiciary and the civil service, and as Supreme Governor of the Church of England, CNN reported, adding that the king is also the Fount of Honour, which means all honors, such as knighthoods, will now be given in his name.

As heir to the throne, Charles was known as a staunch environmentalist and often voiced his concerns about climate change. But as king, his days of advocacy may come to an end. In a 2018 BBC interview, he acknowledged that the responsibilities of his then-current role as Prince of Wales was different from that as a monarch. Asked whether his public campaigning will continue, he said, "No, it won't. I'm not that stupid." 

He expressed similar sentiment, less abrasively, in a pre-recorded, first public address as king on Sept. 9. "My life will of course change as I take up my new responsibilities," Charles said. "It will no longer be possible to give so much of my time and energies to the charities and issues for which I cared so deeply, but I know this important work will go on in the trusted hands of others."