'House of Gucci': Jared Leto's transformation so stunning Al Pacino didn't recognize him on set

You are not the only one who doesn't recognize Jared Leto in House of Gucci.

The shape-shifting, Oscar-winning Dallas Buyers Club actor and musician says one of his own co-stars gave him the cold shoulder on their first day on set together, not realizing the mustachioed bald guy was his screen son.

“The first day I show up to set in character, I went over to Al Pacino and I say hello to him,” Leto tells of us his initial encounter with the 81-year-old screen great (watch above). “And he kind of brushed me off. You could tell he couldn’t wait to get [away from me].

“Somebody whispered to him, ‘Hey, that’s Jared.’ And he fell on the floor basically. His mind was blown, basically. And that moment really carried me through the film.”

Leto sports heavy prosthetics, a deeply receding hairline, a fat suit and lots of pastels to play the eccentric Paolo Gucci in the highly anticipated prestige drama from director Ridley Scott. The film follows the tumultuous story of the famous Italian fashion dynasty amid internal strife that escalates following the marriage of scion Maurizio Gucci (Adam Driver) and Patrizia Reggiani (Lady Gaga), ultimately ending in murder. Pacino plays Paolo’s ambitious father, Aldo Gucci, while Jeremy Irons appears as Aldo’s reserved brother (and Maurizio’s father), Rodolfo Gucci.

“The physical part of it was about six hours in the morning and about an hour at night,” explains Leto, who dropped 30 pounds to play a transgender woman in Dallas Buyers Club (2013) and packed on 67 pounds to play John Lennon’s assassin, Mark David Chapman, in Chapter 27 (2007). “I think the first day, the call time was like 3, 3:45 in the morning. ... But it was great. I really enjoyed the challenge. I enjoy climbing that mountain, as you probably know. I love an immersive process. I love the idea of transformation. Those are things I'm really passionate about.”

His other co-stars were impressed, too.

“It was shocking,” says Driver. “And he’s great in the movie, and the hair and makeup is incredible.” (Indeed, Leto is drawing early Oscar buzz for the role — and you can expect his stylists to get serious awards consideration as well.)

“It was extraordinary because I'd never met him before he came onto the set dressed as he was,” Irons says. “And I looked at him and I couldn't remember how he looked normally … so I just accepted this extraordinary character that he walked on as, and loved his bravery and sort of off the wall-ness.”

House of Gucci opens Nov. 26.

Watch full interviews above, and trailer below:

— Video produced by Jen Kucsak and edited by John Santo