Scene from  'A Star is Born'

Bradley Cooper says there was a scene in A Star Is Born that seemed simple (keyword: seemed) but truly it was a tall order for someone of Lady Gaga's stature to pull off so exquisitely.

Scene from  'A Star is Born'

And it was in that seemingly simplest moment that the 46-year-old actor says his mind was blown away by the triple-threat star.

Scene from  'A Star is Born'

The A Star Is Born star and director shared the intimate detail while chatting with House of Gucci director Ridley Scott in Variety's "Directors on Directors" series.

Scene from  'A Star is Born'

Cooper, of course, starred opposite Lady Gaga, and he directed her as well. She also plays the Italian socialite Patrizia Reggiani in House of Gucci under Scott's direction.

Scene from  'A Star is Born'

While the famed directors traded notes about what it was like to direct the 12-time GRAMMY winner (hint: it was their honor), Cooper brought up their "Shallow" performance onstage. But it wasn't nailing the track that blew him away. Far from it.

Scene from  'A Star is Born'

"I remember the thing that blew my mind," Cooper said. "It seemed simple but I thought it was a tall order, when my character brings [Ally] onstage for the first time. I truly believed that that person had never been on a stage before."

Scene from  'A Star is Born'

Translation: Cooper marveled at the fact that a bona fide global superstar got into character and convinced him that going onstage in front of a packed house was a foreign feeling to her.

Scene from  'A Star is Born'

"And I remember thinking, 'How is she pulling this off?'" Cooper pondered. "That I actually believe on every level -- as the director, as the character -- that this person has never been in front of 20,000 people before. That was really kind of mind-blowing."

Scene from  'A Star is Born'

The 35-year-old actress recently revealed on Entertainment Weekly's The Awardist podcast that it was Cooper who "empowered" her for the role of Ally Maine in the 2018 film.

Scene from  'A Star is Born'

She said that because of that collaboration, it's why she's able to be "where I am now," adding she's now "able to read lots of scripts and talk to lots of different directors."