The first-in-line to the throne, 65, was spotted arriving with his sons to Lancaster House on Thursday morning, where Charles was due to open the conference by giving a speech.
The royal and his eldest son William, 31, have spent the past week campaigning against the illegal wildlife trade. Harry, 29, was keen to show his support for their cause by making a surprise visit to the conference.
As the trio arrived for the event organised by the Foreign Office, they were warmly greeted by foreign secretary William Hague and posed for photos outside the central London mansion.
Charles made no delay in delivering an impassioned speech, in which he highlighted the urgent need to protect endangered species such as elephants, rhinos, tigers and other animals from extinction.
"There is not a moment to lose," Charles told delegates from 50 countries gathered at the meeting. The royal spoke about the importance that elephants, in particular, had for germinating seeds in forests and warned that without the creatures, there would be no forests left.
Charles added that he would organise a follow-up meeting in a month with governments, banks, accounting firms and security agencies to tackle financing behind the organised wildlife crime industry — worth more than six billion pounds each year — and strip poachers of their profits.
During their visit, Charles, William and Harry were shown some of the illegal wildlife items that had been seized at the UK border in Heathrow.
The solutions spoken about in the conference included reducing consumer demand, enforcing tougher laws and helping communities affected by the trade to become sustainable and self sufficient.
The royals' visit comes just a day after William attended a symposium at London's Zoological Society where he gave a speech to urge people to join his foundation, United for Wildlife, to stop illegal wildlife trafficking.
At the start of their week-long campaign, Charles and William released a video message in which they spoke about the "terrible crisis" that was the trade.
As a keen campaigner for wildlife preservation, Charles became president of WWF UK in 2011. Much like his father, William assembled and became president of United for Wildlife, a collaboration of seven global conservation organisations.