The singer, who rekindled her romance with the actor earlier this year, took to the stage at the One Love concert in Malibu, California on Sunday (02Dec18) to encourage audience members to bid on a motorcycle ride and lunch with her beau.
"That also means that when you're on the motorcycle with him, you're holding him in a way that I am not excited about! You're holding his pecs and his six-pack - and it's so glorious!" she told the crowd. "You get to hold on to Orlando for about 45 minutes... And then, you get to stare into his brown eyes!"
A bid then came in for $20,000 from a woman called Laura, at which point Katy shrieked: "Yay! I don't know who you are, but stan for my man!"
However, the jealousy then appeared to be too much to handle, as the 34-year-old jumped in and said: "Laura, I'm sorry - I'm buying it for $50,000."
The auctioneer confirmed the American Idol judge's winning bid as he declared, "Sold - to the lady in the red leather skirt!"
Katy had earlier performed at the charity concert, held at the King Gillette Ranch in Calabasas, which was organized to raise funds following the devastating wildfires in the state of California last month.
Revealing her keyboard player Ty Bailie had lost his home in the blazes, Katy explained: "I'm really here because of this guy. This guy is my friend, and we've been on tour for the past couple of years, and he lost his house in the fires.
"But he's got the greatest attitude and perspective in life and he's the coolest guy, and I'm really just here for him - and for everyone else that has been affected by this horribleness. But we have an opportunity to grow together now. I love you so much."
Other performances at the benefit concert came from Robin Thicke, Alanis Morissette, Rita Ora, and Gwen Stefani, with money raised from the event split between the One Love Malibu fund and The Malibu Foundation.