WASHINGTON (AP) — For nearly six years, a senior Secret Service agent kept his extramarital affair with a Mexican woman a secret from the agency responsible for protecting the president.

But in the wake of an embarrassing prostitution scandal involving 13 agents and officers, Rafael Prieto's secret was revealed by a fellow employee amid concerns that the Secret Service wasn't enforcing its rules consistently.

With an internal investigation ongoing, Prieto apparently committed suicide last week. That's according to people familiar with the matter. They spoke on condition of anonymity because they were not authorized to discuss Prieto's death or the investigation, which they say has focused on whether Prieto violated agency rules that require disclosing relationships with foreigners.

They say Prieto, a married father, admitted the years-long relationship when confronted by investigators.