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The CHOGM family with Queen Elizabeth II in centre, front. Jacinda Ardern is at the far right, second row from the front.

The Queen has formally opened what is likely to be her last Commonwealth Heads of Government Meeting (CHOGM), and could be the last headed by a royal. 

Prime Minister Jacinda Ardern was among 51 of the 53 member states, that was at the poignant opening ceremony. at Buckingham Palace. British Prime Minister Theresa May delivered a statement that honoured the Queen Elizabeth II's dedication to the Commonwealth during her 66-year reign. 

The Queen, who is 91, no longer travels as much and it's only that this year's summit was being held in London that she was able to attend. 

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Britain's Queen Elizabeth II speaks during the formal opening of the Commonwealth Heads of Government Meeting in the ballroom at Buckingham Palace in London.

"I want to offer my heartfelt thanks to Your Majesty Head of the Commonwealth," May said. 

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"Over many years you have been the Commonwealth's most steadfast and fervent champion. You have been true to the deepest values of the Commonwealth - that the voice of the smallest member country is worth precisely as much as that of the largest. " May said. 

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NZ Prime Minister Jacinda Ardern (second left), with partner Clarke Gayford (left) meet Prince Charles and Camilla, Duchess of Cornwall at Clarence House in London, ahead of the opening of CHOGM. Ardern will also have a private audience with the Queen overnight (NZ time).

Following the ceremony, all the leaders were ushered to the palace ballroom for a "family photo". 

Culture and colour was on full display for the photo as the Commonwealth spans a host of Pacific, Caribbean and African countries. Leaders stood in traditional dress of their home countries.

The Queen has lead the Commonwealth since she took the throne in February 1952. Her son the Prince of Wales Prince Charles took his seat beside her at the front of the photo, and gave the formal welcome address to open CHOGM.

The gathering was "a moving reminder of the strong and affectionate bond we all share", said the Prince.

"And so it is I pray that this Commonwealth Heads of Government Meeting, will not only revitalise the bonds between our two countries, but also give the Commonwealth a renewed relevance to all its citizens." 

And to declare the summit officially open, Queen Elizabeth spoke of the Commonwealth's history and the work the Prince would carry on to reinforce the network of countries. 

"Here in Buckingham Palace in 1949 my father met the heads of Government when they ratified the London Declaration, which created the Commonwealth as we know it today. 

"Then Comprising just eight nations. Who then, or in 1952 when I became Head of the Commonwealth, would have guessed that a gathering of a number of states that would one day number 53, or that would comprise 2.4 billion people," she said.

"The Prince of Wales will carry on the important work started by my father in 1949. By continuing to treasure and invigorate our associations and activities I believe we will secure a safer and more more prosperous and sustainable world for those who follow us."

But it does not mean the role of Head of the Commonwealth need necessarily go to Prince Charles when he is made King. 

A range of options are on the table, including having the role skip a generation and pass straight to third in line Prince William or a rotational system whereby country leaders take turns at heading the Commonwealth. 

That would be similar to how the chair of the Commonwealth is chosen. 

Leaders are expected to vote on a decision in London over the next two days. 

Ardern would also meet the Queen in a 20 minute private audience reserved for new Commonwealth leaders. That was scheduled to take place overnight NZ time. Ardern was in two minds however, about whether to offer the Queen condolences over the loss of her last corgi Willow on Saturday.

Ardern's cat Paddles died last year, and the PM was touched when Japanese Prime Minister Shinzo Abe offered his condolences. However Ardern said she would have to give it some consideration as it can be more painful bringing up the loss of a pet. 

 - Stuff