We’re all stunned and saddened by the disclosure that long-trusted and respected state Rep. Brian Ellis finds himself under investigation by the Dauphin County district attorney for a three-year-old allegation of sexual assault.

Several sources told the Philadelphia Inquirer on Thursday that Dauphin County District Attorney Fran Chardo was investigating Ellis, 49. Chardo would not confirm or deny the investigation, citing his office’s policy.

Reaction to the news indicates a widespread disbelief across the 11th District, a constituency Ellis has represented since 2005 — quietly, conservatively and bereft of any incident approaching embarrassment.

But Harrisburg is telling us otherwise. Gov. Tom Wolf, state Victim Advocate Jennifer Storm and the Republican Party leadership caucus give credence to the allegation by calling for Ellis’ resignation.

We reluctantly call for his resignation as well — not as much for the as-yet alleged despicable act as for the disquietude and distraction that will be generated from the allegation itself.

Storm, the victim advocate, has been working with the alleged victim. She suggests some dark details will come to light. “We want to make it very clear that she was not voluntarily intoxicated — this woman was incapacitated,” she said.

Let’s get this straight. The victim advocate says she concluded that the woman was drugged. Isn’t that the felony crime for which comedian Bill Cosby was convicted? That’s a serious allegation — an allegation being investigated by the prosecutor of Dauphin County, home of our state capital Harrisburg.

The severity of it only increases the air of distraction and confusion for the constituents of the 11th legislative district and their representative.

Let’s adhere to due process; presume innocence until proven otherwise. But consider, anything less than innocence would have been a great and distracting burden on one’s conscience over the past three years — a burden that surely would have impeded a public servant’s performance and concentration on his mission in many respects.

The nature of the problem changes, now that it’s disclosed. Whether it’s true or false, the allegation is a great distraction and burden. It will incapacitate Ellis’ ability to perform as a legislator.

He unfortunately has not legitimate choice but to surrender his office at least until the criminal investigation against him is completed.