The booming-voiced 78-year-old had begun to deliver his opening lines in the Shakespearean tragedy when he apparently fainted and fell from a raised platform.
Fellow actor Noel White, who was playing the Earl of Kent, said: “Ladies and gentlemen, this is not part of the play. Is there a doctor in the house?”
Fortunately, a surgeon who was at Monday night’s performance in Holy Trinity Church in Guildford, Surrey, attended to the ex-Z Cars actor on stage in front of the rest of the cast and audience, including his daughter Rosalind, who was playing the part of Goneril.
Blessed – whose career in television, film and stage has spanned six decades – returned 20 minutes later after being clapped off by the audience.
One reviewer said: “After being given a cup of sweetened tea, he returned to the stage after 20 minutes to apologise to the final-preview audience for the interruption.
“Despite waves of dizziness and such shortness of breath that he rolled his eyes and occasionally clutched his chest, he then resumed what soon became one of the more remarkable and moving renditions of Lear of all time.
“Here, indeed, was a ‘poor, weak old man’, as Shakespeare calls Lear, but also a brave and determined stalwart of our English stage. Slowly, step by step, sometimes with a helping hand from his colleagues, often with visible effort, Mr Blessed did battle with his frailty – and won.”
Blessed reportedly said after the performance: “I feel such an idiot and am not in the habit of doing this, but I have little fibrillation.”
At the curtain call, as some other cast members were said to be in tears, he patted his heart and gave a thumbs up gesture.
Director Caroline Devan said: “Brian was an inspirational wonder. He had a small heart operation three years ago. We are not entirely sure why he became so dizzy but he is a 20-year-old in a 78-year-old’s body. There was no stopping him.”
Blessed’s agent, Stephen Gittins, said in a statement: “Brian would like to thank everyone for their concern. The press night was an amazing success. Brian is thrilled to be working with the Guildford Shakespeare Company and is looking forward to the rest of the run.”
Speaking soon after being cast as King Lear, Blessed, when asked how he would be approaching the production, is reported to have said: “I think a big mistake with playing King Lear is to make him too senile. The man has colossal energy levels, so the idea of coming on ancient or old and in a wheelchair is nuts. Mine is much more powerful, I hope – even a touch of Genghis Khan.
“The man is a majestic, powerful creature with great energy – he has a slight heart problem I think and is prone to mental storms. But the main thing is that it must gallop apace. I’ve been to productions that last five and half hours, and that is not on.”
Blessed was born in 1936 in Mexborough, Yorkshire. He left school at the age of 14 and worked as a plasterer and undertaker before training at the Bristol Old Vic Theatre School.
A keen mountaineer, he has climbed Mount Kilimanjaro and became the oldest man to reach the magnetic North Pole on foot.
He tried three times to reach the summit of Everest without oxygen – in 1991, 1993 and 1996 .
Blessed found fame in BBC TV series Z-Cars and later went on to star in Flash Gordon and Kenneth Branagh’s Much Ado About Nothing.