Boris Johnson has been mocked by his sister Rachel after claiming "too often" English was not being spoken as a first language.
Author and journalist Rachel Johnson said she did not know what her brother was talking about, because "we spoke ancient Greek at home".
The would-be prime minister's comments were aimed at immigrants, saying he wanted them to "feel British" and learn English.
But he had already been criticised by Welsh and Gaelic-speaking politicians for his remarks before his sister's intervention.
Johnson tweeted: "We spoke Ancient Greek at home I genuinely don't know what he's on about."
The Tory made the remarks at a hustings in Darlington on Friday.
He said: "I want everybody who comes here and makes their lives here to be and to feel British, that's the most important thing, and to learn English.
"And too often there are parts of our country, and parts of London still and other cities as well, where English is not spoken by some people as their first language, and that needs to be changed and people need to be allowed to take part in the economy and in society in the way that that shared experience would allow."
Gaelic-speaking SNP MP Angus MacNeil said on Twitter: " Boris is just moronic and clueless."
