Nelson Mandela's memorial service will bring together a collection of at least 50 world leaders for what is expected to be one of the biggest gatherings ever known for a head of state.
Such is the influence of the first black South African president, that US President Barack Obama will rub shoulders with Hassan Rouhani, the new Iranian president.
The gathering is likely to present a major security headache for the South African authorities.
The Queen is also understood to have written to Mr Mandela's widow Graca Machel expressing her sympathies.
And Buckingham Palace confirmed that Prince Charles will represent his mother at Mr Mandela's funeral service in Qunu, South Africa on December 15.
Deputy First Minister Martin McGuinness has said he hopes to be there too. He said it would be a "great honour indeed".
"I would certainly like to be there and every effort will be made to ensure we are represented," he said.
"It is important that we honour and respect the memory of Nelson Mandela."
Other guests include former Finnish president Martti Ahtisaari, who helped oversee the decommissioning of IRA arms during the peace process here alongside Cyril Ramaphosa of the ANC.
The former Irish head of state Mary Robinson will join Mr Ahtisaari there as part of the delegation of The Elders, a group of former statesmen which Mr Mandela helped to launch.
Current Irish president Michael D Higgins left for South Africa last night ahead of the funeral accompanied by his wife Sabina.
The Irish government is being represented by Tanaiste and foreign affairs minister Eamon Gilmore.
Separately, a number of former Dunnes Stores workers, who went on strike in the 1980s over the import of goods from apartheid South Africa, also departed for Johannesburg.
The strike in Dublin was triggered in 1984 when 21-year-old cashier Mary Manning was suspended for refusing to handle goods bought from South Africa.
The official memorial service will take place at the FNB Stadium in Johannesburg.
A message on the South African government website said it would be attended by the public as well as heads of state.