Global beverage giant Coca-Cola has apologised for an ill thought-out marketing campaign in Canada after a customer with a developmentally delayed sibling opened a bottle of vitamin water to find that the inside of the bottle cap read “YOU RETARD”.

Blake Loates, photographed the offensive bottle cap and sent the image to her father, Doug Loates, who then wrote a public letter to the beverage giant, Stuff.co.nz reports.

In the letter, Loates explained that his daughter Fiona suffers from both cerebral palsy and autism, has had 22 surgeries and is still fed through a feeding tube.

"Fifty years ago they might have called her retarded. But we know better now, don't we?" he wrote.

"What would YOU do if you opened up your bottle of Vitamin Water and on the bottom of the lid it read: 'YOU RETARD'?

"Think about it. I bet you'd be pissed if you had a Fiona in your life!"

The marketing campaign involved printing random combinations of English and French words under bottle caps and Coca-Cola has since issued a statement apologising for the incident.

Coca-Cola’s director of brand communications Canada, Shannon Denny said that the company takes consumer concerns ‘very seriously’.

"This is a genuine oversight in the review process. The mistake has been corrected and the words removed from all future production," Denny told Canadian broadcast network CNBC.

"Regretfully, the French words were not reviewed from an English standpoint.