RALEIGH, N.C. — Federal authorities investigating John Edwards' campaign finances plan to go to Virginia in the coming weeks along with Edwards' attorneys to  to interview a major donor of the two-time Democratic presidential candidate, a source told WRAL News on Thursday.

A federal grand jury is believed to be looking into whether any of Edwards' campaign funds were used improperly, including whether money was used to hide an affair Edwards had with staffer Rielle Hunter.

Hunter gave birth to a girl in February 2008 who Edwards has admitted is his daughter.

Rachel "Bunny" Mellon, the 100-year-old heiress to the fortunes of both 19th century industrialist Andrew Mellon and the Warner-Lambert pharmaceutical company, now part of Pfizer, was a major political contributor to Edwards in his 2008 presidential campaign.

Mellon gave $3.4 million in late 2007 to The Alliance for a New America, a nonprofit supporting his candidacy. She also gave $700,000 to Andrew Young, a former top aide to Edwards who posed as the father of Hunter's child during the 2008 campaign. The money is said to have been used to pay for expenses incurred by Hunter.

FBI agents have twice visited Mellon's estate in Upperville, Va., to speak with her, sources said. This time, Edwards' attorneys plan on accompanying them to sit in on the interview, a source said.

Mellon's son and two grandsons appeared at the federal courthouse in Raleigh in December to answer questions by the grand jury. Sources said they didn't have information about the money Mellon gave to Edwards but testified about how she might have been pulled into an alleged cover-up of Edwards' affair.

Edwards, a former U.S. senator from North Carolina, has denied wrongdoing.