Veteran actress Margaret Tyzack is to join BBC One soap EastEnders in April, it has been announced.
The 79-year-old will play Lydia Simmonds, the maternal grandmother of Albert Square regular Janine Butcher.
Best known for her classical stage roles, Tyzack has won numerous awards for her stage work including two Oliviers and a Tony.
The actress said she was "delighted to be joining a great British tradition and a fine company of actors".
Viewers will see the snobbish Lydia reunited with Janine, whom she has not seen for years.
Eastenders' executive producer Bryan Kirkwood said it was "a coup" to have her on the show.
Tyzack, he continued, was "an actress of incredible class and talent" whose character had "endless possibilities".
On the small screen, Tyzack is perhaps best known for playing Sir Derek Jacobi's mother Antonia in Roman saga I, Claudius.
She won a Tony in 1991 for her role opposite Dame Maggie Smith in Lettice and Lovage and was seen at the National Theatre in 2009 alongside Dame Helen Mirren in Phedre.
Actress Charlie Brooks has played Janine Butcher in EastEnders since 1999.
The 29-year-old left the BBC One show in 2004 but returned to the ensemble four years later following the death of her on-screen father Frank.