Jo Marney said in a series of text messages to a friend that the Prince's "black American" fiancee will "taint" the British royal family with "her seed" and pave the way for a "black king", according to a report by Britain's Mail on Sunday.
This development prompted UKIP chairman Paul Oakden to announce that Marney's membership in the party has been suspended pending an investigation. "He must go, he must go quickly, he must go as quietly as possible".
"She has to go or he and @UKIP are doomed if we let this behaviour happen in the party", the teenage activist said.
UKIP MEP Bill Etheridge tweeted a statement which said: "Henry does not have the experience, the political nous or advice to deal with the issues he faces".
She said: "The opinions I expressed were deliberately exaggerated in order to make a point and have, to an extent, been taken out of context".
Mr Bolton - who had been accused of covering up his new relationship during the leadership contest - faced demands to step down to limit the damage to the party. If he were to quit, it would leave UKIP seeking its fifth leader in 18 months.
Peter Whittle, leader of Ukip's delegation in the London Assembly, also called for Ms Marney to be "expelled altogether" for the "disgraceful remarks".More news: Liverpool clash pivotal to Manchester City's historic season, claims Pep Guardiola
More news: Payday 2 For The Nintendo Switch Release Date Confirmed
More news: India 80-2 at tea on day two
Mr Oakden said: 'In light of messages that have been brought to my attention, I have taken the decision to immediately suspend her party membership pending an investigation.
He added that he and other UKIP members needed to be "behind our leader 100% in taking that battle forward".
Ukip's National Executive Committee is set to meet on Thursday to decide the party leader's fate.
The pair's relationship became public earlier this month after the Ukip leader confirmed that he had changed his "relationship status" in recent weeks.
Calls for the suspension and expulsion of Jo Marney, who describes herself as a "Presenter".
He claimed that his marriage to Ms Smurova was already over when he met Miss Marney, and has said: 'I have no doubt I'm going to come out of this, and Jo and I are going to come out of this as a couple, stronger than we went into it'.
"They were never meant to be put in the public domain and I'd like to take this opportunity to offer my honest and deepest apologies to anyone I've hurt and for the distress and embarrassment I've caused my family, friends and the party".