"I was taking the kids to school and then the next minute I got a phone call from Dana and they asked about fighting for the interim world title," Hunt told the Herald.
"So it all happened pretty fast and if anyone can do it, I'm your man ... I've always believed I was the best fighter on the planet."
Once again, the deck is stacked against Hunt. He will have to deal with the altitude - Mexico City sits around 2240m above sea level - a fresh Werdum (18-5-1) and the fact that Hunt (10-8-1) needs to lose 17kgs to make the UFC's heavyweight limit of 120.6kg.
Hunt, who had ballooned to 137kg during what he called "family mode", will leave for Mexico tomorrow and his fitness trainer, the Auckland-based Alex Flint, won't be far behind.
"The lucky thing is he carries a lot of water weight because his diet's not great in between fights," Flint said of Hunt. "So he can drop probably seven or eight kilograms quite easily ... Then the rest is just going to have to be three-and-a-half weeks of very hard slog and a very clean diet. That's the only way he can do it."
Hunt's previous fight at altitude was against Ben Rothwell in Denver at UFC 135 in 2011 where he won a unanimous decision but wasn't comfortable with the thin air.
"To acclimatise in three-and-a-half weeks is a huge task but Mark Hunt is Mark Hunt and he's never going to turn anything down," Flint said.
"There's a lot up against him but that's the way he likes it."
Hunt's need to strip weight means he will likely do little sparring in the lead up to the fight as he will focus on his fitness. Hunt's long-time trainer Steve Oliver, who works on his ground game, will join the camp in Mexico next week.
The 1.93m Werdum, a Brazilian jiu-jitsu black belt, has recorded nine of his career wins via submission and is riding a four-fight win streak.
UFC 180, which marks the first time the world's biggest MMA promotion has staged a show in Mexico, sold out in eight hours and more than 20,000 fans are expected to attend.
Given the withdrawal of Velasquez, who has a strong Mexican heritage, punters are allowed to have their tickets refunded but there's a good chance the Mexico City Arena will still be at capacity on fight night.