Mary Lou McDonald said she was sorry for the IRA assassination when she was quizzed on the historic murder following the Duke of Edinburgh’s funeral at Windsor Castle on Saturday.
Lord Mountbatten was killed in 1979 while he was holidaying at his summer home, Classiebawn Castle.
The IRA planted a radio-controlled explosive device in his fishing boat, Shadow V, in Mullaghmore, a small seaside village in County Sligo, Ireland.
Lord Mountbatten was on a trip to go lobster-potting and tuna fishing when the bomb went off.
Watch: Prince Philip remembered, Northern Ireland violence, Sofagate, Biden's corporate tax
Fishermen pulled Mountbatten from the water and tried desperately to save him but he died from his injuries.
The IRA claimed responsibility for the assassination which also killed Lord Mountbatten’s 14-year-old grandson Nicholas, a 15-year-old crew member Paul Maxwell and Doreen, Lady Brabourne, whose son was married to Mountbatten’s eldest daughter.
The IRA maintained that Lord Mountbatten was a legitimate target and former Sinn Fein leader Gerry Adams had previously stood by his comments that Mountbatten “knew the danger” of visiting Ireland in 1979.
But Ms McDonald agreed to apologise to the Prince of Wales for the death of his great uncle on Times Radio: “The army and armed forces associated with Prince Charles carried out many, many violent actions on our island.
“I can say of course I am sorry that happened. Of course, that is heartbreaking. My job, and I think that Prince Charles and others would absolutely appreciate this, my job is to lead from the front, now, in these times.
“I believe it is all our jobs to ensure that no other child, no other family, no matter who they are, suffers the same trauma and heartbreak that was all too common on all sides of this island and beyond.
“I have an absolute responsibility to make sure that no family faces that again and I am happy to reiterate that on the weekend that your Queen buried her beloved husband.”
Lord Mountbatten was regarded as a great mentor to Prince Philip and Prince Charles. Charles often referred to the war hero as his “honorary grandfather”.
Mountbatten counselled Charles on a great many things, most famously his love life.
It was also Lord Mountbatten who had arranged the visit of King George VI and Queen Elizabeth to Dartmouth Royal Naval College on 22 July 1939.
Included in these plans were Princesses Elizabeth and Margaret, who were to be entertained by his nephew, Cadet Prince Philip of Greece while their parents toured the college.
It was the first meeting of the then 13-year old Princess Elizabeth and Prince Philip.
Watch: The wonderful life of Prince Philip, The Duke of Edinburgh