The grandson of the man who ordered the nuclear bombings of Hiroshima and Nagasaki 70 years ago, recalled how he gradually became an advocate of nuclear-free world.

Clifton Truman Daniel is the son of President Harry Truman’s only child – fiction writer Mary Margaret. Clifton’s grandfather apparently visited the family on a regular basis. It wasn’t until he went to school that Clifton found out his grandfather had been the US president, he told RT’s documentary channel RTD.

Daniel learned that the US dropped nuclear bombs on Japan during WWII from history books and for many years felt no personal connection to the pivotal events of the 20th century.

“The bombs were a great thing. They ended the war. They saved hundreds o thousands of lives on both sides and that’s what my grandfather said was his reason for the decision. To shorten the war and save American lives that would likely be lost in an invasion of the main islands. I went from thinking about it in that way to not thinking about it, as I say, it was history,” he recalled.

The attitude changed one day when his son brought a book home from school. It told the story of Sadako Sasaki, who survived the bombing of Hiroshima at the age of two, only to die of radiation-induced leukemia nine years later.

A Japanese legend promises that a wish will be granted to anyone who folds a thousand origami cranes. As Sasaki was battling the decease, she made paper cranes in the hope of getting better. Her wish never granted - she died in 1955, .

“As I said earlier my text book had numbers and reasons and planes and megatons. There wasn’t anything that happened to little girls,” Daniel said. “I went from not giving it much thought at all to being confronted one day with the reality that people lost their lives and in horrible ways and that has sort of brought me to the middle.”

READ MORE: ‘Faceless body belonged to my sister’: Hiroshima, Nagasaki nuke survivors recall horrors 70 years on

Daniel became the first member of the Truman family to visit Japan, when he took part in the commemoration of the victims of the bombings in 2012. He had been invited by Sadako's older brother, Masahiro Sasaki.

The visit had its tough moments, Daniel recalled. For instance when he was interviewed by a Japanese journalist, who repeatedly asked him whether he would apologize for his grandfather’s decision, which he didn’t.

“I don’t know that there’ll ever be an apology. Maybe the two countries can find language that brings them together to say ‘you know we acknowledge that serious hurt was done on both sides and we own that and going forward we pledge not to do something like that’ but it doesn’t feel at this point that there will ever be a flat out apology from the US to Japan or the other way around,” he explained.

Harry Truman acted in good faith and believed he was saving many Americans’ lives, Daniel said. This was the prime consideration for the president, who had first-hand experience of battlefield during World War I and valued soldiers’ lives, he explained.

He admitted that controversy over Truman’s decision remains, as some people believe that the use of nuclear weapons was not necessary.

“The real question which we keep trying to answer but we can’t is did it in fact stop the war. Some people say no, Japan would have surrendered anyway; other people say they were not giving up, it stopped them cold,” Daniel said. “But we can’t know that because we did it and the war ended, so we don’t know how it would have gone.”

“I think that Americans can still look at the decision and they can still say it was done for the right reasons,” he added. “They can also say look what it cost. They can have empathy. It doesn’t take anything away.”