PORTLAND Multnomah County Chair Jeff Cogen announced his resignation Friday.

Cogen will step down Sept. 16 and his appointed designee, Marissa Madrigal, will serve as Chair until a replacement is elected next May. On Wednesday, Madrigal resigned as Cogen's Chief of Staff.

Read the full statement here

I am confident that the county is and will remain in good hands, and that its successes will continue, Cogen said in a statement Friday.

More: Jeff Cogen's chief of staff quits

Cogen's resignation comes in the wake of public scrutiny surrounding his admitted affair with fellow county employee Sonia Manhas.

Cogen is under state investigation regarding his two-year affair with Manhas to determine if there was any criminal wrongdoing. Investigators want to find out if Cogen misused county resources or abused his power.

Background: Records show Cogen doubled lover's county budget request

In July, Manhas resigned from her position as the county health department's policy and planning director and called for Cogen to also resign.

I am deeply sorry that I failed to live up to that trust, and for the pain my actions have caused, Cogen said in his letter Friday.

Cogen's affair with Manhas was revealed after county employees received an anonymous email. The email said that county employees saw the two kissing in front of the Kenton Library and at a bar, among other places.

Timeline: Jeff Cogen scandal

Mayor Charlie Hales said Friday the decision will help Portland move forward.

I wish him well. I wish his family well. He did the right thing, Hales said. The city and the county have a lot of work ahead of us. Jeff s decision today clears the way for our common constituents.

Despite the DOJ's investigation, Cogen was adamant that his affair was nothing more than a personal matter.

I welcomed the investigation and remain confident that it will clear me of these charges, Cogen said.

In an exclusive interview with KGW in July, Cogen said the affair was reckless but he would not resign.

Watch: Laural Porter's full KGW interview with Jeff Cogen

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