The disciplinary letter, issued to former Major John Manning and his subordinate, former Captain Autumn Fowler, demoted both to lieutenant for not disclosing their relationship.
Department policy requires any personal relationships be reported so the department can avoid liability and conflicts of interest.
A Washington State Patrol investigation found the couple's relationship began in January of 2012, but wasn't revealed until late August when another captain discovered the relationship and reported it to the department and Manning's wife.
Manning's attorney suggested a letter of reprimand and brief suspension; however, the chief demoted Manning two ranks, to lieutenant. Fowler was demoted one rank, also to lieutenant. Both will lose proportional salary.
According to Bellevue Police Chief Linda Pillo, the "discipline does not arise from the relationship itself." In her letters reprimanding Manning and Fowler, the chief said their deceit and personal priorities severely damaged trust in their abilities.
Manning and Fowler were reassigned; each will now supervise a patrol squad.
The chief said the fallout of the violations will impact the department for years to come. She added she hopes trust can slowly rebuild.
The incident falls on the heels of another scandal in the Bellevue Police Department.
Two Bellevue police officers were demoted and disciplined last fall after displaying drunken behavior at a Seahawks game in Seattle.