London mayor candidate Zac Mr Goldsmith's defeat was due to an "dog whistle campaign", a senior Conservative peer has said.
Baroness Sayeeda Warsi - a former party chair who was the UK's first female Muslim cabinet minister - said the "appalling" campaign has "lost us the election, our reputation and credibility on issues of race and religion".
Jemima Goldsmith appeared to suggest that her brother's campaign had been shaped by advisers which did "not reflect who I know him to be - an eco-friendly, independent- minded politician with integrity".
She also congratulated Labour's Sadiq Khan after he was elected mayor, calling him a "great example to young Muslims".
In a Facebook post, Mr Goldsmith said he was "disappointed of course by the result" as he thanked his team and volunteers who gave up "so much time" to help his campaign.
He also congratulated Mr Khan and thanked "the hundreds of thousands of people who trusted me with their votes".
Meanwhile, Conservative Assembly member Andrew Boff has said the Goldsmith campaign "seemed to attribute radical tendencies to people of orthodox religious views".
He added: "I think that is a complete misunderstanding of the patchwork of faiths there are in London, and has the potential to alienate people and say that people who do have orthodox religious views, conservative religious views, are for some reason not welcome and won't be listened to."