Outgoing US Secretary of State John Kerry took the powerful step of visiting the place in the Mekong Delta where he was ambushed during the Vietnam War.
Shaking hands with Vo Ban Tam, once a member of the Viet Cong who is now a shrimp and crab farmer, Kerry, a former US Navy lieutenant, admitted it felt surreal revisiting the site where he once shot and killed a man.
But he later tweeted how powerful it was both sides of the war "could now be friends and work towards the same goal of strengthening US-Vietnam relations".
The war between North Vietnam and South Vietnam, which lasted from 1955 until 1975, in which South Vietnam was supported by its main ally, the US, claimed between 1.2-4 million lives, including 58,000 Americans.
Until he met Vo Ban Tam on Friday, Kerry did not know the identity of the dead soldier fighting on behalf of the Viet Cong.
Tam, 70, informed him the deceased was Ba Thanh, aged 24, who "was a good soldier". He was operating a rocket launcher and was shooting at US fighters to get them into range while they were on patrol.
Kerry who was 26 years-old at the time leapt ashore and shot dead the rocket launcher's operator.
Kerry was later awarded the US Army's Silver Star for bravery and other honours of service, but became an anti-war activist following his return from the war in 1969. He faced criticisms for the shooting during his unsuccessful bid to be president in 2004.
He told reporters yesterday, according to a report by news agency AFP: "It impressed on me the notion that you really need to analyse and understand what lies underneath the slogans."
He was visiting Vietnam as part of his last foreign tour as secretary of state before President-elect Donald Trump's inauguration on 20 January, when he will be sworn in as the 45th president of the United States.