Josh Fenton-Glynn will run the 26.2 miles through the capital in memory of his brother, Alex English, who died in January 2025 from a rare cancer.
The King and Queen are due to arrive in the US on Monday for a four-day visit during which they will meet President Trump.
Argentina has long claimed sovereignty over the Falkland Islands and invaded them in 1982 before being defeated in a short but bloody war.
The Sinn Fein vice president delivered the keynote address on the first evening of the Sinn Fein Ard Fheis in Belfast.
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