The "Firework" hitmaker became engaged to Orlando on Valentine's Day, February 14, and the singer admits she had an inkling something was off the moment she laid eyes on the Brit.
"I had to work that day and I just remember meeting him at dinner at this Italian restaurant," she recalled in an interview on the U.K.'s Capital Breakfast With Roman Kemp show, explaining she immediately noticed he was wearing more formal attire than usual and was perfectly groomed.
"I'm like 'Oh s**t, something is going down,'" she said.
Katy's instincts were right - after the romantic dinner, Orlando took his girlfriend on a helicopter ride, where he got down on bended knee.
"Then we landed on this building, went downstairs and my family and my friends were there," she shared.
Orlando's cleaned-up appearance wasn't the only clue Katy picked up on, as the couple was surrounded by the "most flowers" she had ever seen during the special date.
Comparing the elaborate gestures to the lengths Kanye West goes to for his wife Kim Kardashian, she added, "(It's) like when Kanye does that for Kim, you're like, 'Oh, my God!' I was like, 'Oh, my God!' "
The singer previously opened up about Orlando's proposal during an interview on U.S. talk show "Jimmy Kimmel Live!" in late February, when she revealed his helicopter surprise didn't quite go to plan as he struggled to pull the large ring box out of his pocket, and ended up ripping his jacket lining, as he elbowed a bottle of Champagne.
Despite the mishap, Katy insisted the proposal was "really sweet".
The couple, which has been dating on and off since early 2017, has yet to reveal its wedding plans.
The marriage won't be the first for either star. Katy was previously wed to Russell Brand from 2010 to 2012, while Orlando was married to Victoria's Secret model Miranda Kerr from 2010 until 2013. The exes are parents to son Flynn, eight.