Sir Antony Sher has been diagnosed with a terminal illness, the Royal Shakespeare Company (RSC) says.
The 72-year-old is widely regarded as one of the country's finest contemporary classical actors and has a long association with the company.
The RSC said its artistic director and Sir Antony's husband, Gregory Doran, had taken compassionate leave to care for him.
Sir Antony's film appearances include Shakespeare in Love and Mrs Brown.
RSC credits include Richard III and Macbeth. He also appeared in TV series including The History Man and the BBC's Murphy's Law.
South African-raised Sir Antony joined the RSC in 1982, winning an Olivier Award in 1985 for Richard III.
He became an honorary associate artist with the company, based in Stratford-upon-Avon in Warwickshire.
In 2010, he told the BBC about his first visit to the RSC and described it as one of the most significant experiences of his life.
Sir Antony was knighted in 2000, and in 2005, with Mr Doran, became one of the first gay couples to enter into a civil partnership in the UK.
Mr Doran said: "I am very sorry to say that my husband, Tony Sher, has been diagnosed with a terminal illness, and in order to look after him, and with the agreement of the Board, I will be taking a period of compassionate leave with immediate effect. I expect to return in early 2022."
The actor Eddie Marsan tweeted he was sending his love to the couple.
He wrote that when he worked with Sir Antony "I was blown away by his amazing commitment, talent and kindness".
Sending all my love and best wishes to Anthony Sher and his husband Greg Doran at this difficult time. When I worked with Anthony I was blown away by his amazing commitment, talent and kindness.— Eddie Marsan (@eddiemarsan) September 10, 2021
The head of Arts Council England, Darren Henley, said Sir Antony's illness was sad news and added he and Mr Doran had "created an awe-inspiring body of work" at the RSC.
Very sad news. The thoughts of all of us at @ace_national are with you. Together, Sir Antony Sher and Gregory Doran have created an awe-inspiring body of work at @TheRSC over many years. Death of a Salesman in 2015 was one of my personal highlights. But there are many, many more. https://t.co/mYFKxdG9zb— Darren Henley (@HENLEYDARREN) September 10, 2021
The RSC said its deputy artistic director Erica Whyman would take over Mr Doran's role until his return.
Company chairman Nigel Hugill said: "All our thoughts are very much with Greg and Tony at this extremely difficult time."