So what inspired the Queen of Halloween to dress as a 95-year-old woman?
"There was so much talk about me turning 40 this year and what it felt like to be older," Klum told PEOPLE. "I thought, really? I will show you old!"
The supermodel worked with Oscar-winning makeup artist and friend Bill Corso for the transformation. "He came to my house and casted my face," says Klum, who chronicled the process for her Instagram fans.
"The rest of my ideas – the grey hair, yellow-stained teeth, lots of wrinkles, a hunchback, arthritic hands, age spots and milky eyes – he just made happen!"
Gregg DeGuire / WireImage
The day after Halloween, Klum Tweeted a photo of her prosthetics, thanking special effects pro Andy Clement.
Known for taking the spooky holiday to extremes, Klum said, "I like to surprise my guests and to encourage them to go all out, as well."
This year's party attendees included Ice T and Coco, Bethenny Frankel, Jay Manuel and Victoria Secret's model Lindsay Ellingson.
In fact, Klum was almost unrecognizable upon arriving at Marquee nightclub on Thursday. She acted in character on the red carpet, joking with reporters about her get up: "It didn't take a long time at all," she said, in a little old lady voice. "I put on a little bit of eye shadow and my dancing shoes and I was ready to go!"
That, obviously, was the point.
"Life is serious enough as it is," Klum said. "It is great to be someone else for the night and let loose."