Bryn Terfel recently played Sweeney Todd at the Royal Albert Hall

The Welsh star said he was "deeply sorry", but had faced a "stressful situation" with one of his children which affected his preparations.

Terfel had already begun rehearsals to play Wotan in the Wagner epic, which opens later this month.

The Royal Opera, in London's Covent Garden, said it was "shocked and surprised" at the singer's decision.

Complete Cycle

Sir John Tomlinson, who was sharing the role with Terfel, has agreed to take on all of his performances.

The singer's statement, which was released through his agent, said: "Having begun rehearsals it is clear to me that I would not be able to perform at the standard I would wish to.

"Rather than progressing through rehearsal in the hope that I might make it, I feel it is better for The Royal Opera and the fantastic team working on this epic production that I withdraw at this stage," added the star.