The move will increase pressure on Rishi Sunak to attend the global meeting after the prime minister initially said he would not go.
Mr Sunak has since left open the possibility of attending, with a No 10 spokesman saying it would depend on progress with the autumn budget statement.
Mr Johnson told Sky News he had been invited by Egypt, following the UK’s role as host of last year’s talks, and was “very happy to be going”.
He said, “I happen to have a special interest.”
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