The mug shows Prince Harry and Middleton instead of Prince William.
The mug can be seen on the company's website, http://guandongenterprisesltd.com.
The mug was supposedly designed by a Chinese company, but the UK Telegraph newspaper discovered that the company is actually registered in Britain.
That's raising the question if the gaffe was intentional, either to sell the mug as a gag item or as a collectible with a "mistake."
Sometimes items with errors become more valuable.