Treacy revealed that the collaboration was the fashion-loving Born This Way star's idea - and he was thrilled to have her on board.
"I went to see Lady Gaga backstage after seeing her at Twickenham [for the Born This Way Ball tour], and I was telling her about the show and then she just suggested it. It was all her idea. She was going to be in Dublin the night before, so she said that she'd fly over for it. Playing to 80,000 people on one night and then appearing in my show the next? Amazing. Of course I agreed," he told Vogue. "She had this whole concept, she said she was feeling like Isabella. She rang me on her way to the show to apologise for being late - you never see that any more. She really is like a 21st Century pop version of Isabella Blow."
Treacy also praised Gaga for her unique take on fashion.
The singer is known for her eccentric outfits and her perception of style allowed the milliner to go all out with his designs.
"She's a really fun person to work with," he continued. "She has a different sensibility - a different idea of what's perfect and beautiful. She allows me to be really creative and brings my designs to a whole new audience."
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