"It was like, if we were gonna do a tuxedo, it couldn't just be a tuxedo," Siriano said during an interview with E! "It needed to be a moment. Billy wanted something different, wanted to push the boundaries. I don't think any man has really worn a gown on the Oscars red carpet before, and Billy was the person to do it. He was really giving a moment."
While Porter's extravagant gown looks like it took months to design, fit and perfect, Siriano said he threw it all together in just one week.
"Listen, we had no time. One week!" he said. "I fit his stylist's assistant in this dress because [Billy] was here. He had no time! Fit perfectly, no alterations, you're welcome!"
Of the actual garment, Siriano explained it was a "classic tuxedo shirt, jacket that's cropped and a bow." Layered underneath was a "strapless, corseted gown."
"The whole idea was that he felt like it was about androgyny," Siriano explained. "There are no rules in fashion. You can be whoever you wanna be and wear what you wanna wear. I think fashion is for anyone. Put on whatever you want that makes you feel good, and that's what it's all about."
The 2019 Oscars aired live from the Dolby Theatre in Hollywood, California, Sunday at 8 p.m. ET / 5 p.m. PT.