London (CNN) The sister of British Prime Minister Boris Johnson has condemned his rhetoric as "tasteless" and "reprehensible" as he faced a storm about his language in the UK Parliament.

Rachel Johnson said she did not recognize the version of her brother that spoke in the House of Commons on Wednesday evening.

Boris Johnson faced sharp criticism for his language as he addressed Members of Parliament on Wednesday, their first day back after his controversial suspension was ruled illegal by the Supreme Court.

Johnson repeatedly denounced legislation that would force him to delay Brexit if he can't agree a deal with the EU, calling it a "surrender bill." And he dismissed as "humbug" the concerns of an MP who asked him to moderate his language given the politically motivated murder three years ago of a Labour lawmaker, Jo Cox.

The Prime Minister provoked particular anger when he urged lawmakers to honor Cox's memory by backing the government on Brexit. (Cox was a supporter of staying in the European Union.)

Rachel Johnson, second left, pictured with brothers Boris and Jo in 2014.

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