Ma Weishuo and his wife, taken in late 1970s.[Photo by Li Bing/China Daily]

Chen Jiaji, a Guangdong native who became interested in the story of Dean Lung after watching a TV documentary in 2009, was among the first to see the letters.

"I spent most of the past 10 years in South Africa and returned to Guangzhou late last year and have been there since because of the COVID-19 outbreak," he says.

With a lot of spare time suddenly available, Chen decided to revisit his old interest and joined an online group formed by him, Huang Xiangguang and a number of others. They call it the Dean Lung Search Team.

The Chinese letter is believed to have been penned in Taishan by Ma Weishuo, the son of Ma Wanchang, to his own two sons in the US.

"When he was young, your grandfather was driven by poverty to seek his fortune in the United States," says the letter, written entirely in traditional Chinese, with one exception. "He eventually set foot in New York and entered the employment of a rich American. He gave himself a new name, Ma Jinlong－Mar Dean Lung."

The writer had taken the trouble to spell out his father's late-acquired name both in Chinese (Ma Jinlong) and in English (Mar Dean Lung). Ma Jinlong is the Chinese name's spelling in pinyin, the phonetic symbols used for the romanization of Chinese characters, adopted by the Chinese mainland in the 1950s.

Among other details, Ma Weishuo went on to talk about the donation of $10,000 to Columbia University by his father, and a chair in which the name "Mar Dean Lung" is carved that can be found in the university auditorium.

A few lines earlier Ma Weishuo wrote:"Accompanying my words is an English letter－what has remained of the correspondence between your grandfather and that rich American. Since I don't know what it is talking about, I'm sending it to you."