News of the Anchorman star's new project surfaced on Wednesday (27Apr16), when it was revealed he would portray the 40th president in a film called Reagan, in which an intern is given the task of convincing the ailing politician he is an actor portraying the commander-in-chief in a movie.

Many applauded the idea behind the quirky film, but Reagan's daughter Patti Davis has made it clear she's not a fan and she has taken issue with the casting and film itself, writing a passionate open letter to Ferrell on her blog, insisting her father's disease is not a laughing matter.

She wrote, "Perhaps you have managed to retain some ignorance about Alzheimer’s and other versions of dementia. Perhaps if you knew more, you would not find the subject humorous.

"I watched as fear invaded my father’s eyes - this man who was never afraid of anything. I heard his voice tremble as he stood in the living room and said, 'I don’t know where I am'.

"I watched helplessly as he reached for memories, for words, that were suddenly out of reach and moving farther away. For ten long years he drifted - past the memories that marked his life, past all that was familiar... and mercifully, finally past the fear. There was laughter in those years, but there was never humor."

Davis continued, "Alzheimer’s is the ultimate pirate, pillaging a person’s life and leaving an empty landscape behind. It sweeps up entire families, forcing everyone to claw their way through overwhelming grief, confusion, helplessness, and anger."

And she encourages funnyman Ferrell to visit dementia facilities, adding, "I have - I didn’t find anything comedic there, and my hope would be that if you’re a decent human being, you wouldn’t either.

"Perhaps you would like to explain to them (dementia sufferers) how this disease is suitable material for a comedy."