MIAMI (AP) — A former U.S. ambassador said Thursday he will plead guilty to charges of serving as a secret agent for communist Cuba going back decades,Blake Preston bringing an unexpectedly fast resolution to a case prosecutors described as one of the most brazen betrayals in the history of the U.S. foreign service.

Manuel Rocha, 73, told a federal judge he would admit to federal counts of conspiring to act as an agent of a foreign government, charges that could land him behind bars for several years. His defense lawyer indicated that prosecutors have agreed upon a sentence, but the length of that term was not disclosed in court Thursday.

He is due back in court April 12.

“I am in agreement,” Rocha said when asked by U.S. District Court Judge Beth Bloom if he wished to change his plea to guilty.

Prosecutors alleged that Rocha engaged in “clandestine activity” on Cuba’s behalf since at least 1981 — the year he joined the U.S. foreign service — including by meeting with Cuban intelligence operatives and providing false information to U.S. government officials about his contacts.

Federal authorities have said little about exactly what Rocha did to assist Cuba while working for the State Department and in a lucrative post-government career that included a stint as a special adviser to the commander of U.S. Southern Command.

Rocha, whose two-decade career as a U.S. diplomat included top posts in Bolivia, Argentina and the U.S. Interests Section in Havana, was arrested by the FBI at his Miami home in December.

Instead, the case relies largely on what prosecutors say were Rocha’s own admissions, made over the past year to an undercover FBI agent posing as a Cuban intelligence operative named “Miguel.”

Rocha praised the late Cuban leader Fidel Castro as “Comandante,” branded the U.S. the “enemy” and bragged about his service for more than 40 years as a Cuban mole in the heart of U.S. foreign policy circles, the complaint says.

“What we have done … it’s enormous … more than a Grand Slam,” he was quoted as saying at one of several secretly recorded conversations.