The BBC reported that the agenda for the meeting included a time for "wider governance consideration", which is reportedly code for discussion of succession plans.
The alliance of former British territories appointed Queen Elizabeth II as its chief upon her coronation in 1953 - taking over the role from her dad, King George VI - but there are no rules that will automatically pass the title to the 91-year-old's heir when she dies.
The Commonwealth has launched into secret talks considering who might succeed the Queen as its head.
While there may not be an alternative to Charles within the royal family, and therefore he could assume the position by default, it has also been suggested that Commonwealth Heads may opt to have an elected ceremonial leader in a bid to improve the organisation's image and democratic accountability, as this has been previously discussed.
While the issue of succession is not listed in the group's mandate, senior sources told the BBC that the succession would be discussed at the gathering.
Greece's Queen Anne Marie, left, talks to former Spanish Queen Sofia, right, and Britain's Prince Charles while attending the funeral ceremony in tribute to late Romanian King Michael in Bucharest, Romania.
A "high-level" Commonwealth group is meeting amid reports it will discuss the Queen's succession.
A source told the BBC that the group would discuss whether there should be a one-off decision to appoint Prince Charles or whether it should develop a new process to ensure a British monarch always heads the Commonwealth.
In April, the Commonwealth Heads of Government Meeting (CHOGM) is being staged in London and Windsor.
Speaking about riding in an extravagant horse-drawn golden carriage that carried her from Westminster Abbey through the streets of London back to Buckingham Palace - the mother-of-four admitted it wasn't as stunning as it appeared.
The Queen has been working to ensure it is Charles that succeeds her. It will look at how the secretariat is run and funded, how a new secretary general is chosen and the balance of power between the Commonwealth's governors and executive committee.
According to documents seen by BBC, the high-level group will not just confine itself to bureaucratic changes.
As well as Mr Tong, the group consists of Lord Howell, former British energy secretary; Louise Frechette, former United Nations Deputy Secretary General; Robert Hill, former Australian defence minister; Dame Billie Miller, former Deputy Prime Minister of Barbados; Dr Ngozi Okonjo-Iweala, former Nigerian finance minister; and George Vella, former Deputy Prime Minister of Malta.
The group, which has its own staff and budget, is independent of the Commonwealth Secretariat. A whole section of his website is devoted to the Commonwealth, noting that he has visited 41 out of 53 countries and has been a "proud supporter" for more than four decades.