The FBI's former number two, W Mark Felt, has claimed to have been the mystery Deep Throat source who helped bring down US president Richard Nixon.
Mr Felt, 91, told Vanity Fair magazine: "I'm the guy they used to call Deep Throat."
Lawyer John O'Connor, who wrote the article, said Felt had revealed he was the source who leaked secrets about Nixon's Watergate cover-up.
Unmasking the identity of "Deep Throat," a key source for Post reporters Bob Woodward and Carl Bernstein, would solve one of the greatest political and journalistic mysteries of recent history.
The magazine said Felt, now a retiree living in Santa Rosa, California, had admitted his role in the scandal to his family and had cooperated with the story. It is the first time a major potential source has claimed to be "Deep Throat."