Bradley Cooper wore late composer Leonard Bernstein's personal bathrobe in 'Maestro'.

The Jewish conductor's children Jamie, Alexander and Nina threw the doors open to their family home in Fairfield, Connecticut for the 48-year-old actor to film scenes for the biopic and even gave him the dressing gown to add to realism.

Speaking to Variety, Jamie said of the actor's transformation into her father: “It took our breath away, it made us gasp.

“In some pictures, we could tell a little bit that it was Bradley, but there were certain photographs where we would go, ‘Oh my God!’ It was so amazingly perfect.”

Nina couldn't tell the difference when the 'A Star Is Born' star video-called her.

She said: “I had a FaceTime call come in, and I didn’t recognise the number. But I chanced it, and it was my father as an old man!

“Obviously, that was not my father as an old man, it was Bradley. I could not stop laughing. He had the cigarette and the glasses, it was so spot on.”

Not only did Bradley wear his robe, but the children sent him home with their father's medicine case and co-star Carey Mulligan, who played Bernstein's wife Felicia got to keep her gold cigarette lighter.

Jamie continued: “We literally opened our doors to Bradley and his team."

Carey, 38, also got to wear one of Felicia's gowns.

Quizzed on whether Bradley got to wear or use anything belonging to the maestro himself, his eldest daughter added: “There was a bathrobe that he actually wore in some of the footage.

“And there was a dress of our mother’s that Carey wore.”

The family has nothing but praise for Bradley's work on the film - which he also directed - however, there has been some controversy surrounding the prosthetic nose he wore for the part of the legendary Jewish star and Jamie is frustrated by the backlash.

She told Vanity Fair magazine: "It's just such an annoying distraction. The people who were waiting to get mad about something were just waiting to pounce."

Bradley worked with Oscar-winning makeup artist Kazu Hiro to create the controversial nose and Jamie, along with her siblings Alexander and Nina, were amazed by the resemblance he had to their father.

She explained: "It just made us gasp at what they were able to achieve. He would send us photographs on his phone, and some of them were so spot on that we would think, 'Oh, come on now, he just sneaked in a picture of our dad.'"

The prosthetic had been described as an "annoying distraction".