In the 1960s, celebrated American playwright Arthur Miller had a son, Daniel, who was diagnosed with Down syndrome.

But you won't find any mention of Daniel in Miller's memoir, speeches or even in the obituary of his mother, the famous photojournalist, Inge Morath. The family never publicly acknowledged Daniel's existence.

Hello: I'm Arthur Miller's Unknown Child is the final installment in Vancouver-playwright Susanna Uchatius' theatrical trilogy that follows the tragic story of the young boy who grew up in an institution for people with mental illnesses.

"Daniel was in a horrible institution, it really was horrendous at that time," Uchatius told Sheryl MacKay, host of CBC's North by Northwest. 

About half a dozen actors with cognitive challenges tried out for the role of Daniel, but Uchatius settled on her own daughter, Alex Edwards.

"I have brain damage and sometimes I have a hard time saying words," said Edwards.

"There's hard words I cannot say, my mouth cannot say," she explained before demonstrating how she's practiced saying words like "institution."

Daniel's story first told in 2007

The mother-daughter team worked out a system where they would break long or difficult words into parts. Edwards learns one part at a time until she can string all the syllables together.

In a way, the two have been performing together for years. Edwards couldn't speak clearly until she was 5 or 6 so she would act out what she wanted to communicate while standing on a stool.

"She really taught me how vocal the body is," said Uchatius. "I'm always humbled by Alex. She is one my best teachers." she said.

The idea to tell Daniel's story first came to her thanks to a 2007 Vanity Fair article that revealed for the first time how the family hid Daniel's identity and much of his life story.

It was published two years after Miller's death and contrasted the many glowing posthumous accolades showered on Miller with the secret abandonment of his own cognitively challenged son.

Celebrated as moralist

In the obituaries that followed his death,  Miller was lauded for his award-winning work, including The Crucible and Death of a Salesman. He was celebrated as a moralist and a hero.

While he kept Daniel a secret for decades, it was revealed weeks after Miller's death that he had named his son as an heir in a document that accompanying his final will.

Uchatius says Hello isn't about judging Miller's actions, rather about trying to understand if those actions matter to the rest of society.

"Does it just matter to me as the mother of a child with a cognitive difference? To me it's a question of the value of humanity," she said.

Edwards said she is looking forward to seeing how the audience reacts to Daniel's story.

"Will there be any tears or love? What will they feel from the heart when they watch this performance?" she asked.

Hello: I am Arthur Miller's Unknown Child runs May 5th to 13th at Vancouver's KW Studios.

With files from North by Northwest