Heidi Klum Debuts Out-of-This-World Halloween Costume After a More Than 12 Hour Transformation

The supermodel and TV star shared every step of her transformation into a nightmarish alien for Halloween.

It turns out that the process of going from an iconic supermodel to a nightmarish vision of terror and grotesque body horror takes at least 12 hours, if not more.

Heidi Klum decided to go all-out once again for her over-the-top Halloween costume this year, and she brought fans along for the ride, sharing snapshots of the various steps that went into the long, labor-intensive process.

After 12 very long hours, the transformation was complete, just in time for her star-studded 20th Annual Halloween Party at Cathédrale New York, which included a slew of famous stars decked out for the special occasion, including Ice T, Coco Austin, Dylan Sprouse, Barbara Palvin, Questlove, Maluma and many others.

Klum's grand entrance, however, was next-level intense as she was driven to the event in a trailer with glass walls, covered in biohazard symbols, along with her husband, Tom Kaulitz, who was decked out like an astronaut, covered in blood with a shattered space helmet.

Klum, in all her nightmarish glory as a menacing alien, growled at people as they were driven up to the event, and the lady of the evening spoke with ET's Rachel Smith, where she and Kaulitz revealed the bizarre, sci-fi backstory behind her creepy character.

"So I was on a mission in outer space, looking for a new planet, because we almost destroyed ours," Kaulitz explained. "So I found her and I brought her back, because I thought she might have some useful information for us."

Taylor Hill/Getty Images

"I totally lost track of time today. I don't even know how long this took for me today," Klum added.

"This year was easy. I was done in like four hours. So nothing compared to Shrek," Kaulitz revealed of his costume last year. "I asked for a costume that took a little less time."

For fans who happened to be in New York, Klum gave them a look at the incredible makeup FX process in person, as she sat in a chair in the window of the Amazon store on W. 34th street, where a crowd gathered to watch her become an undead, half-cybernetic abomination.

"Let’s get this party started!" Klum wrote on Thursday morning, sharing a photo from the chair that she'd be seated at for nearly the entire day.

She shared photos and videos of the process, from getting her hair pulled back to the initial applications of latex prosthetics. She even shared a stomach-churning photo of herself, partially zombified, chowing down on a big bowl of noodles.

Along the way she also got a special supportive visit from her husband and her longtime friend and Project Runway co-star Tim Gunn.

"My real husband plus my tv husband came to visit me," Klum gleefully captioned one of the many videos.

The update videos continued throughout the night as the truly gruesome costume really started to come together in all its freakish glory. From exposed internal organs to metallic-looking biomechanical implants, Klum's costume got increasingly horrific and impressive as the posts kept coming and the hours kept ticking by.

By the time she'd been getting made up for 12 full hours -- and they'd finished coloring the latex monster skin and attached the exposed brain case -- it seemed Klum was getting a little fatigued, writing, "Still here ?"

Speaking with ET at the Halloween party, Klum reflected on what it was like getting ready in front of a giant window where fans could watch the process.

"I loved it," Klum marveled. "Because all the fans, all the people who love Halloween and love costumes, those were the people that came by... [and] they could finally see what these amazing makeup artists do for a living all the time in the movie industry, and normally people don't get to see this kind of stuff."