WASHINGTON -- A former spokesman for David Petraeus says the retired U.S. general's affair with a female biographer started after Petraeus left the Army.

Retired Army Col. Steve Boylan tells ABC that Petraeus' wife of 38 years, Holly, is "furious" over the matter. Boylan also says that Petraeus' affair with Paula Broadwell ended four months ago.

Petraeus, who resigned as CIA director on Friday, acknowledged the affair in a letter to agency employees.

Boylan on Monday said Petraeus' wife "is not exactly pleased right now. Furious would be an understatement."

Boylan, who says he spoke with Petraeus over the weekend, tells NBC that Petraeus is "devastated." Boylan says "it's going to take a long time" for him to set things straight at home.