In an interview with BBC Radio 4, Tony nominee Simon Russell Beale, who plays the title role in the Sam Mendes-helmed production, said, because he had few scenes with Troughton, he was one of the last to know what was happening.
He first learned of it, he said, when Mendes "whizzed past backstage and said Troughton had lost his voice."
Beale said some cast members thought the silence was a deliberate choice at first, and they continued with the performance. He said, "There were things he had to do, so we had to nip and tuck on the wing... Various actors had to do monologues, so it was rather skilful."
During the play's intermission Mendes explained to the audience that Troughton had lost his voice and the understudy, Paapa Essiedu, would take over the role for the remainder of the performance.
"I went and saw him at the interval and just patted [Essiedu] on the back because the last thing he wants is me wishing him well... but he was fantastically cool," said Beale.
"It's one of those occasions when you go: 'I'm rather proud of this team for just willing it forward.'"
Troughton will return to play Edmund on Thursday's press night.