A Harrods security guard said the Range Rover arrived at the department store with the graffiti already scrawled on it.
But others were less sceptical.
Property developer Stephen Halford, 55, said: “The car was parked opposite Harrods.
“I think the wife had sprayed the Range Rover and drove it there parked in one of the most conspicuous places in London in the heart of Knightsbridge.
“There was a large crowd gathering and everyone was taking photos and messaging their friends. It seemed to brigthen people's days and a bit of street justice was seen to be done.
“Everyone was applauding the lady, I think she is a class act.”
Revenge: The car was daubed with the words "cheater"
Stephen Halford
Many witnesses also took to Twitter to air their views.
One woman posted: "Oh my, that's one way to get back at him...! Hell hath no fury like a woman scorned."
A man said: "Note to self don't #cheat this just happened", while another wrote: “If you think your having a bad day...” accompanied with pictures of the car."
Do you know the owner of the car? Contact the Standard newsdesk on 020 3615 2534.