-- From Times staff reporter Sara Jean Green:

A 54-year-old Eastside woman has been charged with first-degree incest after authorities said she had a two-year sexual relationship with the adult son she had given up for adoption when he was an infant.

Katheryn M. Thornton invited her son, now 33, to come live with her at her home near Kirkland in March 2004 after he tracked her down through an adoption agency, according to charging papers filed in King County Superior Court earlier this month.

In May, the man reported the alleged incest to a King County sheriff's detective. He told the detective that the day after he moved in, Thornton "came into his room and lay next to him. He said day three, she invited him into her room. He said on day four, they had sex," the charging papers say.

The man said his sexual relationship with Thornton lasted until March 2006, according to the charges.

The son, who is not being named because he is considered a victim of sexual assault, was granted a sexual assault protection order against Thornton on Tuesday, barring her from coming within 500 feet of him, his home, school or workplace, court records show. Thornton was briefly booked into the King County Jail on Tuesday morning before being given a conditional release, according to jail records.

First-degree incest is a Class B felony. If convicted, Thornton would face a 12- to 14-month prison sentence and be required to register as a sex offender.