The recordings were recorded in 1992 and 1993 between Diana and actor Peter Stellin, who was trained in vocal casting skills at Kensington Palace in London.
Channel 4 says the recordings provided a "special vision," but Diana Munkton, Diana's close friend, said her broadcast was a violation of her privacy.
Moncton, who told the station not to broadcast the tapes, told the Guardian that those details "do not belong to the public domain."
"It would be a betrayal of her privacy and the privacy of her family," she said.
Stellen had recovered the recordings in 2004 after a dispute with Earl Spencer, the late princess' brother after British police confiscated records in 2001 from the house of the former princess's servant, who was accused of stealing some of Diana's property.
NBC broadcast footage of the recordings in 2004, as the BBC was planning to broadcast in 2007 on the 10th anniversary of Diana's death, but retracted its decision.
This comes as Prince Earl Spencer, brother of Diana, asked the British channel not to broadcast those recordings.