Speaking about the show stopping ensemble, Petra said: "The entire dress was hand beaded onto lace. It took over 1,700 hours and a team of 11 from the Givenchy Atelier. It's a beaded wonder. When you see it up close it's a marvel of various golden colours, shapes and sizes.
And the flame-haired beauty was also on board the creative process, although she initially imagined the floor-length fringed piece to be in silver rather than gold.
The fashion guru explained: "During a trip to Paris earlier in the year we saw the beading samples and we selected the beautiful gold, amber and crystal colours."
The popular romantic movie, which scooped four prizes at the prestigious ceremony including Best Director for Damien Chazelle and Best Original Score, was the main source of inspiration for Emma's outfit for the evening.
Petra explained: "I was very inspired by 'La La Land'. The element of dancing, movement and Hollywood glamour definitely got to me. Both Emma and I wanted to capture this feeling in the dress."
As Emma picked up her award, she paid tribute to her fellow nominees Meryl Streep, Ruth Negga, Isabelle Huppert and Natalie Portman, as well as her co-star Ryan Gosling in her acceptance speech.
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Speaking at the time, she said: "To the women in this category you were all so extraordinary and I look up to you and admire you.
"It has been the greatest honour to stand alongside you.
"Ryan Gosling, thank you for making me laugh and always raising the bar and being the best partner on this crazy adventure."