McDonald's has lost its exclusive claim to the "Mc" trademark on some of its food products within the EU after a dispute with an Irish fast food chain.
Supermac's, which owns more than 100 fast food restaurants in Ireland, complained to the European Union Intellectual Property Office (EUIPO).
The EUIPO ruled McDonald's had not proved genuine use of the "Mc" prefix on some of the products it trademarked.
However, the EUIPO upheld McDonald's right to own the "Mc" trademark on chicken nuggets and some of its sandwich products.
The ruling also stated that as both firms had succeeded in some parts of the case and failed on others, each party must pay its own costs.
Supermac's was founded by Galway businessman Pat McDonagh in 1978 and is now the largest Irish-owned fast food restaurant firm in the Republic of Ireland.
Mr McDonagh, who previously referred to his global fast food rival as "McBully," said the latest ruling was a "victory for small businesses".
"The Mc is back," he declared in a company statement.
"McDonald's tried to argue that because they had some products that started with Mc, that the term Mc was so synonymous with them, that they had the right to own and trademark Mc," he added.
"We are delighted that the EUIPO found in our favour and that we can now say that we have rid Europe of the McDonald's self-styled monopoly of the term Mc."
'Core menu items'
However, a statement from McDonald's pointed out that the EUIPO ruling had reinforced its ownership of the Mc trademark on a selection of its fast food products.
"The EUIPO upheld McDonald's EU registration for the trademark "Mc" standing alone for certain core menu items which McDonald's uses in connection with its famous family of Mc-prefixed trademarks," the US firm's statement said.
"This decision does not impact McDonald's ability to use its Mc-prefixed trademarks or other trademarks throughout Europe and the world, and McDonald's will continue to enforce its rights."
Supermac's took the case after a branding dispute halted the Irish company's attempts to expand its restaurant chain into the UK and Europe.
McDonald's had won an earlier battle over the similarity between the name Supermac's and the Big Mac.
Supermac's then asked the EUIPO to rule on the issue and the Irish firm won a partial victory in January 2019.
At that time, the EUIPO ruled that McDonald's had not proved genuine use of the trademarked term "Big Mac" as a burger or restaurant name.
The latest EUIPO ruling revokes McDonald's automatic trademark rights to the use of the term "Mc" on a long list of food products, drinks and restaurant services within the EU.
However, the EU body upheld the US firm's right to own the "Mc" trademark on chicken nuggets and a range of its sandwich products including meat, fish, pork and chicken sandwiches.
McDonald's had argued that due to its long and continuous use of the 'Mc' term, the trademark had become widely and exclusively associated with McDonald's by EU consumers.
The US firm also pointed to several earlier decisions in its favour issued by courts and trade mark offices throughout Europe.
But Supermac's argued that 'Mc' was a "very common prefix for surnames throughout Ireland, the United Kingdom and elsewhere throughout the European Union".
It pointed out that there were a huge number of pubs, hotels, restaurants, and food products which contain the prefix 'Mc' as part of a surname.
The Irish firm claimed that McDonald's had never used the prefix 'Mc' in a standalone sense, but only in combination with other words to brand their products.
"It is not a 'Mc' chicken sandwich, it is a 'McChicken' sandwich," the document states.
The EUIPO agreed with Supermac's that there was no evidence of use of the contested trademark 'Mc' alone, but "only accompanied by further elements".