"This was not something he had just read out of a book."
The event honoured winners of the Princess Diana Awards, established in memory of William and Harry's mother. It's celebrating its 20th anniversary this year.
Ojo said Prince William had spent time reading up on all of the winners before the event, taking care to speak with each one at the afternoon tea.
Venant was one of the award recipients from across the UK and Commonwealth countries, such as Canada, Tanzania, India and Nigeria, who have made a significant impact on society.
Venant received an award for leading a national anti-microbial resistance campaign in 23 Tanzanian regions. The campaign reached nearly 50,000 students and teachers across 114 secondary schools.
Ojo revealed that Prince William told the young people that his mother Diana "would be so proud" of all of them.
The awards were presented by Diana's brother Earl Spencer in a ceremony at the Old Royal Naval College in Greenwich, in southeast London.
It's believed the prince is not fluent in Swahili, as he taught himself the language during his time at university.
William flexed his language skills last year during a royal visit to Tanzania, where he was seen on camera speaking Swahili in conversation with Tanzanian President John Magufuli.
The Duke is believed to speak a total of five different languages, including Welsh, Gaelic, French, and some Spanish.
