The Washington National Opera’s new season begins on September 15th, a week from Sunday, with one of the most monumental operas in the repertory: Wagner’s “Tristan und Isolde.” This weekend, WNO suddenly learned it was going to have to come up with a new Isolde. Deborah Voigt, whose face graces posters for the new season all over the city, has pulled out of the production.

No fear, though: Irene Theorin, a Swedish soprano and experienced Isolde who’s familiar to WNO audiences after fine outings in “Siegfried,” the concert performance of “Götterdämmerung,” and “Ariadne auf Naxos,” will replace Voigt for most of the performances, starting with the opening afternoon. The exception is the final performance on September 27; that will be performed by Alwyn Mellor.

Twilight of the goddess: One of Deborah Voigt’s last outings as Isolde, in 2010. She has withdrawn from the Washington National Opera’s upcoming production and is considering retiring the role from her repertoire.

“Returning to a role that I love but haven’t sung in a number of seasons, and encountering its unique challenges, has caused me to reconsider keeping it in my repertoire,” said Ms. Voigt in a press statement. “I’m very disappointed that I feel compelled to withdraw from this production, but am very happy to continue my association with WNO both this season and into the future.”

Isolde is a legendarily tough role, only sung by the largest of voices. Although Voigt has long been heralded by some critics and administrators as a dramatic soprano in the making, her shining voice in fact has always sounded best suited to the slightly lighter German repertoire. The Empress in Strauss’s “Frau ohne Schatten,” or Sieglinde in Wagner’s “Die Walküre,” or Chrysothemis in Strauss’s “Elektra” are all roles I thought fit her like a glove. Many aver that Voigt’s voice diminished after her weight-loss surgery in 2004, but others -- myself included -- believe that it is simply a question of vocal size. Isolde and Brünnhilde are roles for the largest voices in the repertoire, and neither role has ever been quite right for her, although she recently sang Brünnhilde in Robert Lepage’s much-debated production of the Ring at the Metropolitan Opera, to mixed reviews.

Her next operatic roles, after a string of recitals over the rest of this calendar year, are Leonore in Beethoven’s “Fidelio” in Belgium in January and February, and Marie in Alban Berg’s “Wozzeck” at the Metropolitan Opera in March. The latter is a first for her - and a much lighter role.

Voigt is serving, this season, as the first-ever artist-in-residence with WNO’s Domingo-Cafritz young artist program; she will continue in that capacity. Maybe she can help educate the young singers about one of the most difficult things she has just done: learning when to say no.