Nadine Dorries said she does not fancy the prime minister in an interview on Sunday.
The culture secretary, a long-term ally of Boris Johnson, was responding to questions about why she has supported the prime minister for so long.
LBC presenter Rachel Johnson, who is the prime minister’s sister, said: “I’ve got to ask – perhaps I’m the only person who can ask – but you do look at my brother in a particular way, I’m sure the listeners have seen the memes – the adoring memes.”
Dorries groaned, and claimed: “I’ve had that so many times!
“I look at Keir Starmer in the same way and no-one ever does memes of that, do they?”
The presenter said: “What do you see in him?”
“First of all, I don’t fancy your brother – not a bit,” she added.
“He’ll be gutted,” Johnson replied, to which Dorries said: “I think he knows.”
The culture secretary said she has been pushing for Johnson to become the prime minister since 2012, as she has “always seen the potential in him”.
“It was absolutely obvious, he was always going to be the person who got the Conservatives the kind of majority they deserved and also have the radical agenda we needed to get things done that needed to be done.”
Dorries has been a loyal and particularly vocal defender of the prime minister.
She suggested that Johnson will never be ousted from No.10 through a vote of confidence earlier this year, even as letters of no confidence in Johnson were being handed in by Tory MPs.
Dorries also claimed the general public do not “give a fig” about the resignation of Johnson’s ethics adviser, which shook Westminster last week.
Lord Geidt quit after alleging the prime minister was making a “mockery” of the ministerial code through the partygate saga.
She said: “You call him Lord Geidt. I think the rest of the country had never even heard of him before and called him Lord Geddit.
“I don’t think they give a fig who replaces him or who he was or what he did. It’s a bit of a bizarre one isn’t it? Someone who wasn’t elected who has resigned.
“Everybody thought for 24 hours that he was going to resign over something that was going to compromise the prime minister, was suddenly blindsided by the fact that it was something to do with steel tariffs.”
There has been some confusion over why Geidt resigned, with some claiming that it was over steel tariffs.
However, The Telegraph reported over the weekend that Geidt said this reason was a “distraction” from the root causes of his decision to leave his post.