The discovery of a medieval stone coffin -- with another lead coffin inside it -- was made at a dig at the Grey Friars site in Leicester where the medieval king was discovered in September 2012, the University of Leicester reported Sunday.
The fully intact stone coffin with its included lead coffin is believed to contain one of the friary's founders or a medieval monk, the researchers said.
The inner lead coffin has been moved to the University's School of Archaeology and Ancient History, where tests will be carried out to find the safest way of opening it without damaging the remains within, they said.
Taken from the 7-foot outer coffin, the inner coffin likely contains a high-status burial, possibly one of three prestigious figures known to be buried at the friary.
These include two leaders of the English Grey Friars order and a 14th century knight, Sir William de Moton of Peckleton, who was a mayor of Leicester.
"The stone coffin was always the big thing we wanted to investigate during this dig," Mathew Morris, director of the University's Archaeological Services, said. "For me, it was as exciting as finding Richard III. We still don't know who is inside -- so there is still a question mark over it.
"None of us in the team have ever seen a lead coffin within a stone coffin before. We will now need to work out how to open it safely, as we don't want to damage the contents when we are opening the lid," he said.