A Kirkland woman charged with incest for having sex with her adult son she gave up for adoption as an infant, pleaded not guilty Tuesday morning at King County Superior Court.

The 33-year-old son told King County detectives in May he had a two-year sexual relationship with his biological mother when he re-connected with her through an adoption agency in 2004.

According to charging documents filed earlier this month, 54-year-old Katheryn Thornton invited her son to come live with her and she said his presence made her feel “excited.” She also admitted to having sex with her son for 18 months at her home in the Kingsgate neighborhood of Kirkland’s annexation area.

The son said his mother’s younger children knew he slept in Thornton’s bedroom, but they did not know about the sex, according to the documents.

The woman was briefly jailed on Tuesday, then released. She could face a year in prison and be required to register as a sex offender if convicted.

Thornton returns to court for a case setting hearing on Sept. 14.