Queen Elizabeth II's Platinum Jubilee is in full swing.

The official birthday of the queen kicked off Thursday with Trooping the Colour and the lighting of the beacons. Friday's main event is the Service of Thanksgiving. Queen Elizabeth herself will not be attending the event due to "some discomfort."

The Service of Thanksgiving is one event of many to occur throughout the week and weekend as Britain celebrates 70 years of Queen Elizabeth II's reign. It follows Silver, Gold and Diamond Jubilee celebrations in 1977, 2002 and 2012, which marked 25, 50 and 60 years on the throne. Jubilees are usually marked with a combination of ceremonial military displays, a church service and street parties.

The events began on June 2 and will continue through June 5.

Queen Elizabeth celebrates her Diamond Jubilee

Queen Elizabeth II waves as she leaves a Service Of Thanksgiving at St Paul's Cathedral on the 60th anniversary of her ascension to the British throne. (Photo by Matt Cardy)

QUEEN ELIZABETH THROUGH THE YEARS

WHAT IS IT?

The Service of Thanksgiving is a church service and will take place at St. Paul's Cathedral. 

"The Service will include bible readings, anthems, prayers and congregational hymns, expressing thankfulness for The Queen’s reign, faith and service; desire to foster unity and peace amongst all peoples; and commitment to care for God’s creation," according to St. Paul's Cathedral website.

The venue has also opened an exhibition exploring past Jubilee celebrations held at St. Paul's Cathedral. The exhibit opened on May 25.

Queen Elizabeth waves during the Service of Thanksgiving

Queen Elizabeth II arrives at St Paul's Cathedral for a service of Thanksgiving held in honor of her 80th birthday in 2006. (Photo by Tim Graham Photo Library)

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WHO ATTENDS?

Queen Elizabeth II, although the guest of honor, will not be in attendance at Friday's Service of Thanksgiving due to "some discomfort." The queen has been taking a step back from events as she deals with "episodic mobility issues."

Queen Elizabeth and other royals on the balcony of Buckingham Palace

Prince Charles, Prince of Wales, Queen Elizabeth II, Prince William, Duke of Cambridge and Catherine, Duchess of Cambridge on the balcony of Buckingham Palace during the finale of the Queen's Diamond Jubilee celebrations on June 5, 2012. (Photo by Stefan Wermuth - WPA Pool via Getty Images)

Prince Andrew will also not be in attendance after testing positive for COVID-19 for the second time.

"After undertaking a routine test, the duke has tested positive for COVID and with regret will no longer be attending tomorrow’s service," a Buckingham Palace spokesperson announced on Thursday.

Prince Charles, Prince William and Kate Middleton are expected to attend. Along with Prince Harry and Meghan Markle.

Prince Harry, Meghan Markle and Prince Andrew were not present on the balcony during Trooping the Colour on Thursday due to their lack of working senior royal status.

"The theme of public service is at the heart of today's event," a press release from the palace reads. "Over 400 people have been invited in recognition of their contribution to public life at both a community and national level." 

Additionally, "Lord Lieutenants will also attend the Service to represent every country of the UK, alongside the Prime Minister, Members of the Cabinet, First Minster of the Devolved Governments, Leaders of The Opposition as well as former Prime Ministers." Reps from overseas territories and governors general will also attend among others. 

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The Associated Press contributed to this report.