McGregor throws first punch, lands Twitter jab on Mayweather

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The highly anticipated mega-fight between Conor McGregor and Floyd Mayweather Jr is official, which means their incessant social media trash talk now is, too.

With Wednesday's announcement that Mayweather - the undefeated welterweight boxer - will come out of retirement to face McGregor - a mixed-martial arts superstar - in a first-of-its-kind cross-trade boxing match, both took to their Twitter handles to seal it with a kiss.

The outspoken pair will meet in Las Vegas on August 26.

But UFC champion McGregor seized the opportunity to throw the first punch.

The picture is of none other than 64-year-old Floyd Mayweather Sr, a humorous dig at Floyd Jr -who is no longer a spring chicken at 40.

McGregor is 12 years younger, so he is within his right to make all the old man jokes that come to mind. He had already gotten started earlier this week.

The fighters are set to do battle at the MGM Grand Garden Arena.

Until then, expect much more of the same from both sides.