The cat returned to the mistress of Lib Dem MP John Hemming as been exposed as an imposter.
The Birmingham Yardley MP was initially celebrating on Tuesday after he thought his lover Emily Cox had been reunited with the cat ('Beauty').
The pet had been stolen from Cox's home by Hemming's aggrieved wife Christine and had not been seen since.
But the identity of the cat was called into question by the Cats Protection organisation who studied before and after photos.
Field veterinary officer Vanessa Howie said there were too many differences.
“The cat in one of the images has white paws and a white bib, whereas the cat in the other photo does not," she said.
“Due to genetics a cat’s coat colour and markings are set from birth so the marking patterns don’t change.
“There is also a noticeable difference between the stripes on both photos. These factors indicate these are two different cats.”
A disappointed Hemming conceded: “We have probably not got the right cat. We have not got to the bottom of it yet.
“This cat has had a home for the last year and we have been offered one of its kittens. So, we will probably take one of those.”
In October John Hemming posted an offer of a reward for her return on his blog. "Kitten Missing." he wrote. "If anyone has seen this kitten please contact me at the House of Commons. There is a reward for its return".
Christine Hemming was given a nine-month suspended sentence at Birmingham Crown court on Friday for the theft of the cat. The 53-year-old was given 150 hours of community service and will pay costs of £1,000.