In a three-page personal letter he wrote to Soros six years ago to seek the support of his then-nemesis for his Perdana Leadership Foundation's global anti-war efforts, Mahathir recalled the unforgettable incident in Alor Setar during the Japanese invasion of Malaya.
"The bayoneting death of a young British soldier by the Japanese in my hometown had left a lasting impression on me," Mahathir wrote in his Jan 11, 2006 letter, a copy of which is with Malaysiakini.
"It may seem a minor incident but I cried for this young boy, 8,000 miles from home and family, feeling the bayonet piercing his body. And he screamed two or three times. And then there was silence.
"I was a teenager and I could not help imagining the thing happening to me. How could we kill people so cruelly and feel no sense of guilt."
According to author Barry Wain in his book, Malaysia Maverick, this was one of the traumatic events that shattered Mahathir's teenage innocence, and "thoroughly politicised him and changed the course of his life".
Horrors of war
Soros himself is no stranger to the horrors of war.
Born in Budapest, Hungary, to a Jewish family, he survived the Battle of Budapest, where German and Soviet troops fought house-to-house during the last days of the Second World War.
In 1947, still a teen, Soros migrated to post-war England.
Mahathir had written to Soros to urge the much-maligned currency speculator to join him in his Global Peace Forum, which sought to criminalise war and outlaw it as an option to settle international conflicts.
"I write to invite you to lend your name to this effort to achieve the ultimate human rights - the right to life," Mahathir says in his Jan 11, 2006 letter.
Both octogenarians - Mahathir is 87 and Soros, 82 - have had a bitter war of words, with Mahathir calling Soros a "moron" and blaming the currency speculator for igniting the 1997-98 Asian financial crisis, while Soros hit back by describing the Malaysian premier as a "menace to his country".
Mahathir also says in the letter: "We regard killing a person as a crime punishable with the most extreme punishment.
"It seems to me hypocritical - on the one hand, regarding killing as murder and a serious crime, and at the same time training our young men to kill people, ordering them to kill and glorifying their deeds."
In highlighting their common war-time experiences both men had witnessed when they were in their teens, Mahathir had hope that the billionaire philanthropist would "lend his name" to the global anti-war movement.
"Whatever may be the differences between us, we seem to have identical views on war, i.e. on killing people in the pursuit of a national agenda."
It is not known what Soros had said in his response to Mahathir, but it is likely to have been a polite "no", given that he did not join the Global Peace Forum.
Mahathir met with Soros in Kuala Lumpur 11 months after his letter to the billionaire financier, during which the two foes buried the hatchet.
Following the meeting, Mahathir said he accepted that Soros was not involved in the devaluation of Malaysia's currency.
However, four days ago, Mahathir dug up the hatchet and took another stab at Soros, claiming that the international financier was seeking regime change in Malaysia.
The enmity between Mahathir and Soros can be traced back to the early 1990s when Bank Negara Malaysia - then considered by financial observers as a rogue central bank for dabbling heavily in high-risk currency speculation - lost a whopping RM5.7 billion to the likes of Soros.