Peter Polycarpou is joining the cast of Man of La Mancha, alongside the previously announced Kelsey Grammer and Danielle de Niese.
He will play Sancho Panza in the show, which runs from April 26 for six weeks at the London Coliseum.
The cast also includes Nicholas Lyndhurst and Cassidy Janson, alongside others including Eugene McCoy, Lucy St Louis and David Seadon-Young.
Man of La Mancha is directed by Lonny Price, who directed Sunset Boulevard at the Coliseum starring Glenn Close, which was also produced by Michael Grade and Michael Linnit.
It has music by Mitch Leigh, lyrics by Joe Darion and book by Dale Wasserman.
The show is conducted by David White, with set design by James Noone, lighting design by Rick Fisher, sound design by Mick Potter and casting by David Grindrod.