Actor Benedict Cumberbatch was left with egg on his face after calling black people "coloured" on a US television.
Ironically, he was speaking on a talkshow to highlight the need for greater diversity on British TV and films.
The 38-year-old ex-public schoolboy said he was "devastated to have caused offence by using this outmoded terminology.
"I offer my sincere apologies.
"I make no excuse for being an idiot and know the damage is done."
The Imitation Game actor originally made his comments on a US talkshow hosted by Tavis Smiley, saying: "I think as far as coloured actors go it gets really difficult in the UK, and a lot of my friends have had more opportunities here (in the US) than in the UK and that's something that needs to change."
The Oscar nominee came in for criticism on Twitter, with D'Arcy Lindsay, writing: "Benedict Cumberbatch tries to stick up for black actors and then calls them 'coloured' #cringe".
Continuing his apology, Cumberbatch said: "I can only hope this incident will highlight the need for correct usage of terminology that is accurate and inoffensive.
"The most shaming aspect of this for me is that I was talking about racial inequality in the performing arts in the UK and the need for rapid improvements in our industry when I used the term.
"I feel the complete fool I am and while I am sorry to have offended people and to learn from my mistakes in such a public manner please be assured I have.
"I apologise again to anyone who I offended for this thoughtless use of inappropriate language about an issue which affects friends of mine and which I care about deeply."
A spokesperson for the anti-racism charity Show Racism the Red Card, told the Independent: "Benedict Cumberbatch has highlighted a very important issue within the entertainment industry and within society. In doing so, he has also inadvertently highlighted the issue of appropriate terminology and the evolution of language."
The actor played the role of a slave owner in the film 12 Years A Slave, and has ancestors who owned slaves before the slave trade was abolished.
He has spoken of his family's past as slave owners. During the 18th century, the Cumberbatches were one of Britain's wealthiest families, owning at least seven Barbados sugar plantations.