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McGregor took on Campbell at a Ring of Truth event at the Ringside Boxing Club in his hometown of Dublin, Ireland.
The video shows McGregor, 18, without his tattoos and looking a lot thinner than he did for his last UFC bout.
But you can see his trademark style during the contest as he bounces around the ring, oozing with confidence as he lets his patented left hand go.
McGregor drops Campbell with a big shot before securing the stoppage victory moments later thanks to a blistering sequence.
He stalked his opponent then landed a serious combination. He tagged Campbell hard with a left and right hand before striking him with another brutal right hand to earn the win.
McGregor turned professional a year later as he showed a glimpse of his future. Of course, he went onto win numerous titles across different promotions.
He made his name in Cage Warriors as he claimed the CWFC featherweight and lightweight belts.
'The Notorious' then made UFC history by becoming the first fighter to hold two titles in two different divisions, simultaneously.
He then lured Floyd Mayweather out of retirement to a mega Las Vegas showdown which saw him pocket a reported $85 million.
The 32-year-old, meanwhile, made a return to the UFC this year before announcing a shock retirement in June.
Many think that the retirement won't last and one of those men is UFC president Dana White.
He admitted he sees McGregor making a return to the octagon - but not for the rest of 2020.
"This year, he is retired," White said on the "My Mom's Basement" podcast, as per ESPN.
"He doesn't have a fight this year, and he won't have a fight this year. Conor McGregor will not fight in 2020. ... I guarantee he will not fight in 2020.
"I'm not focused on anything with anybody who's not fighting. Conor McGregor is retired. Do we all believe he'll stay retired? I think most of us don't believe he'll remain retired."
Featured Image Credit: Severe MMA/YouTube
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