According to the BBC, the Royal Opera learned that the Welsh baritone would not be able to sing Wotan only hours before the final performance of Das Rheingold, the first installment in the company's new Ring cycle, directed by Keith Warner.
ROH officials contacted the agent for Donald McIntyre, a veteran bass-baritone who had sung Wotan many times, and the agent reached McIntyre by mobile phone as he stepped off a plane at Gatwick Airport. The singer agreed to fill in, but being unfamiliar with Warner's staging, could not perform Wotan from the stage. Instead, he sang the role in the orchestra pit while Terfel acted the role.
"I couldn't really hear the other singers," McIntyre said. "I was under the front of the stage and when they got a little bit back on the stage I was literally unable to hear a thing."
"I actually had my score with me because the orchestra sounded a lot different to what it does normally," he added.
A spokesperson for the ROH told the BBC that audience members were aware of the unusual arrangement. "The audience were quite excited when they discovered what was happening," he said. "It created an extraordinary frisson in the auditorium."