Bedford has been advised by his doctors not to continue in the production due to illness. He is currently in the hospital receiving treatment.
O'Callaghan created the part of Pope John Paul I opposite David Suchet in the London production of Confession at the Theatre Royal Haymarket. Suchet will also co-star in the upcoming production of this new thriller.
In a statement producer Paul Elliott said, "It is a great shame that Brian Bedford cannot be with us for this unique adventure; we wish him a good and swift recovery. We are fortunate and excited to have Richard O'Callaghan reprising his acclaimed London performance."
Written by Roger Crane, The Last Confession, according to press notes, is a "thriller that delves into the most highly guarded institution in the world to explore the mystery shrouding the sudden death of Pope John Paul I in 1978.
The Last Confession will play the The Royal Alexandra Theatre April 18-June 1.
For more information and tickets visit mirvish.com.