The US businesswoman at the centre of a misconduct controversy involving Boris Johnson has said he "cast me aside like I am some gremlin".
It is alleged that Jennifer Arcuri received favourable treatment during Mr Johnson's time as mayor of London due to their friendship, claims he denies.
Ms Arcuri told ITV she had kept his "secrets" but that her requests to him for media advice had been "blocked".
The Conservatives say any claims of impropriety are "unfounded".
During the interview to be aired later, Ms Arcuri addressed the now prime minister directly, saying: "I've been nothing but loyal, faithful, supportive, and a true confidante of yours.
"I've kept your secrets, and I've been your friend.
"And I don't understand why you've blocked me and ignored me as if I was some fleeting one-night stand or some girl that you picked up at a bar because I wasn't - and you know that.
"And I'm terribly heartbroken by the way that you have cast me aside like I am some gremlin."
Her latest interview, follows allegations, first reported in the Sunday Times in September, that Ms Arcuri's business was given £126,000 in public money along with privileged access to three foreign trade trips led by Mr Johnson when he was mayor, between 2008 and 2016.
The Greater London Authority (GLA) - whose job it is to oversee the conduct of the mayor - launched an investigation into the alleged conflict of interest following the paper's report.
That probe was paused after the authority referred the claims to the police watchdog, the Independent Office for Police Conduct (IOPC).
The watchdog will now decide whether or not to investigate the prime minister for a potential criminal offence of misconduct in public office - before the GLA decides whether to continue its own probe.
Last month, a government review ruled that a £100,000 government grant given to Ms Arcuri's business was "appropriate".
Ms Arcuri said she had tried to ask Mr Johnson for advice on how to handle media attention over the allegations, but was left feeling "humiliated" after being told "there are bigger things at stake" by an aide.
She added: "I was brushed off as if I was one of Kennedy's girlfriends showing up to his White House switchboard, you know, here to do my, you know, calling".
Ms Arcuri would not be drawn on the nature of their relationship during the interview, but said that she had come under pressure from friends to "admit the affair".
In response to the programme, the Conservative Party said it considered the decision to refer Mr Johnson to the police watchdog as "vexatious and politically motivated".
A spokesman added that any claims of impropriety in office by Mr Johnson were "untrue and unfounded".
- 22 September: The Sunday Times publishes allegations about Mr Johnson's friendship with Ms Arcuri
- 24 September: The London Assembly gives Mr Johnson 14 days to provide "details and a timeline of contact" with Ms Arcuri
- 27 September: The monitoring officer of the Greater London Authority refers Mr Johnson to the Independent Office for Police Conduct
- 29 September: Mr Johnson denies any wrongdoing and tells BBC News everything was done "with full propriety"
- 7 October: Ms Arcuri tells ITV's Good Morning Britain programme she "never spoke" to Boris Johnson for help to secure any grants or sponsorship for her company
- 9 October: The London Assembly says a response it received from Number 10 does not answer its questions
- 31 October: Government rules the £100,000 grant given to Jennifer Arcuri's company was "appropriate"