The 32-year-old hit back-to-back 900s on Run 2 and claimed silver at her fifth Games, a joyful moment after finishing 11th in Sochi and seventh in PyeongChang.
"All the emotions just exploded at the end," she told Olympics.com in Beijing.
"And today was amazing even though I didn't start on the right foot, on the second run everything came out, the nerves, the pressure, my thoughts of how important this is and somehow the strength came as well.
"Somehow I managed to put it all together in the second run and make it happen."
Fourth in qualifying the day before the final, Catellet seized the day and this is the peak of a lifetime's work.
"I have been working on it so much and just enjoy and make my riding happen and that's what it was and I couldn't be happier.
"I did a run that I wanted to do and it just worked out with second place which is still amazing after Chloe, she's an incredible rider, an incredible athlete."
Queralt Castellet: Injuries, loss of her partner, pain, and an Olympic podium
Her silver medal is Spain's first Beijing, a Spanish woman's best ever result at the Olympic Winter Games, just the latest in a career of firsts for Castellet.
Her silver at the 2015 Worlds was Spain's first snowboarding medal at a world champs, and she is now the most decorated Spanish snowboarder and winter athlete in history.
But it hasn't been easy.
She's broken her wrist, her jaw, dislocated her shoulder, been forced to withdraw from competition due to concussion - all sustained in crashes in training or competition.
Surgery, recovery, physio, pain, comebacks. Queralt has been through it all to get where she is, but perhaps the most painful of all was losing her partner, coach and boyfriend Ben Jolly in 2015.
He died a year after being diagnosed with brain cancer.
"I spent half a year without touching a board, living at my parents' place in Sabadell. I did not know what to do, I was lost. Nothing was the same as before hence I had to reconsider everything," she said.
A Swiss coach managed to convince her to get back on the board.
"That's where I saw I had to continue on. (Snowboarding) was what made me smile and be happy."
In New Zealand she revamped her routines and rediscovered her love for the sport training with coach Benjamin Bright, who encouraged her to compete in big air too.
Now she's coached by two-time Olympic silver medalist Danny Kaas.
"If there's something I get out of these Games it's that nothing good comes easy," she continued to Olympics.com in Beijing.
"And we are made for passing obstacles and for learning from them and to be grateful of everything we've got and learn from every step of our lives."
Asked how she thought her partner who she lost in 2016 would feel she said:
"I think everyone would be very happy about my result today. From every stone I've found on the way I managed to learn something from it."
So what's next?
"Next up is to celebrate this with my family, my friends, and celebrate something so unbelievable"
"I'm super grateful to have them by my side and it's thanks to that I am where I am."