LONDON — Seeking to salve an old wound at a time of sorrow for Britain’s royal family, the political leader of the Irish republican movement apologized on Sunday for the 1979 assassination of Louis Mountbatten, an uncle of Prince Philip.
Mary Lou McDonald, the leader of Sinn Fein, which was once the political wing of the underground Irish Republican Army, told a London radio station, “Of course, I am sorry that happened; of course, that is heartbreaking.”
Ms. McDonald offered the landmark apology a day after Queen Elizabeth II buried her husband, Philip, in a ceremony at Windsor Castle that paid tribute to his military career. His uncle Lord Mountbatten, a celebrated commander during World War II who later served as the last viceroy of India, overseeing its partition and transition to independence, was killed after a bomb exploded on his fishing boat off the coast of Ireland.
The assassination, carried out by members of the I.R.A., was one of the highest-profile attacks during the Northern Ireland Troubles, and the one that struck closest to the heart of the royal family. In addition to his ties to Philip, Lord Mountbatten was friendly with the queen and a mentor to the couple’s eldest son, Prince Charles.
In elections last year, Sinn Fein won roughly the same number of seats in Parliament as each of Ireland’s two establishment parties, Fianna Fail and Fine Gael. Since neither wanted to form a government with Sinn Fein — in part because of its I.R.A. legacy — they agreed to enter into a formal governing coalition for the first time.