Jo Marney said she “didn’t mean to cause offence”, but she insisted: “I meant what I said that there is an issue with illegal immigration in this country.”
She added: “The language that I used wasn’t good and I didn’t mean to cause offence.”
Sitting alongside Mr Bolton, who left his wife and two children before Christmas, the pair were asked by ITV’s This Morning hosts whether they “private racists” after a series of controversial comments made by Ms Marney.
Ms Marney said it was “disgusting” that Grenfell survivors without leave to remain in the UK at the time of the tragedy were being offered leave to remain.
“That entire tower was a nest of illegal immigrants of all varieties," she wrote on Facebook, shortly after the June tragedy which claimed the lives of 71 people. "That’s why they can’t identify most of them. Meanwhile, British families wait on the Council Housing list for years."
The 25-year-old called her comments on Ms Markle and Prince Harry’s upcoming wedding “disgusting” and said they were not reflective of her views.
“Who can realistically say they have never said anything offensive in private?” she told presenters Philip Schofield and Holly Willoughby.
Mr Bolton also defended Ms Marney’s controversial remarks, saying her posts about Grenfell had been taken out of context and it was right to raise the issue of illegal immigration at the tower.
“Jo has used emotive language, but actually they shouldn’t allow that to take away from the problem,” he said.
The 54-year-old, who has now quit Ukip, said rivals within the party had used his relationship to oust him.
Mr Bolton was voted out as leader at the weekend, five months after his leadership victory.
Interim Ukip leader Gerard Batten said Mr Bolton’s resignation “will draw a line under a sad period” for the party.