Tulisa Contostavlos has said she is "outraged" at her conviction for assaulting a celebrity blogger at a music festival.
The former X-Factor judge was convicted of hitting Savvas Morgan during an altercation at V-Festival in Chelmsford.
The ruling was made by a judge at Stratford Magistrates' Court in east London today.
Earlier this week, a separate drugs trial against Contostavlos, 26, collapsed after the judge said there were "strong grounds" to believe that undercover reporter Mazher Mahmood - known as the Fake Sheikh - had lied in the witness box.
Contostavlos, who wore a blue suit, white shirt and nude stilettos, shook her head and smiled in disbelief as today's guilty verdict for assault was read out.
Standing on the steps of the court building, she declared that she was "outraged" at the conviction and vowed to clear her name in an appeal.
Mr Morgan, who suffered swelling to his eye, said in a statement that he felt "vindicated" by the verdict.
Contostavlos was ordered by the court to pay a total of £3,020. This consisted of a £2,700 contribution towards the cost of the prosecution, a £200 fine, £100 compensation to Mr Morgan and a £20 victim surcharge.
Her assistant, Gareth Varey, 28, was cleared of using threatening behaviour during the incident, which occurred at the V Festival in Chelmsford in the early hours of August 18 last year.
Contostavlos, of Royal Drive, Friern Barnet, north London, claimed during the trial that Mr Morgan had a ''strange obsession'' with her.
She told the court that he had conducted a ''vendetta'' against her since an incident in which she asked security to remove him from a VIP area at the Whisky Mist nightclub in London's Mayfair.
The former N-Dubz singer also outlined her suspicions that he was involved in the release of a sex tape of her online.
The prosecution case was that, when Mr Morgan was leaving the festival site, he found himself to be following Contostavlos and her friends, including Mr Varey.
It was suggested that former Sugababes star Mutya Buena was with the group and called back to Mr Morgan to ask him to join them.
But Contostavlos angrily told him to stop following her. She then raised her fists in the air and hit him in the face.
District Judge Angus Hamilton said: ''I am quite sure to the requisite standard of proof, based on my analysis of the evidence that I have heard, that Ms Contostavlos did strike Mr Morgan in the face during an argument and that that blow caused minor bruising and swelling.''
The trial, which previously took place at Chelmsford Magistrates' Court, heard that Buena, rapper Misha B, singer Alexandra Burke and rapper Wretch 32, all witnessed the incident but have not given evidence.
In a defiant statement after today's guilty verdict, Contostavlos said: "This has been a rollercoaster week for me. I never wanted any of this. I did not assault Vas J Morgan and I am outraged at this decision. I will be appealing it.
"There are a number of high-profile witnesses who were there and know what happened. I urge them to come forward and tell the truth at the appeal.
"I am determined to clear my name as I have already done once this week. I repeat - I did not assault Vas J Morgan. I am innocent."
Mr Morgan - who has joined the cast of ITV2 series The Only Way Is Essex - said after the conclusion of the case: "I'm pleased we can finally put an end to this and move on.
"It's been a difficult time for everyone involved and I'd just like to put it behind me. I've had my character questioned and now feel vindicated by the verdict."
Jeremy Dein QC, barrister for Contostavlos, said in mitigation that his client was provoked by the actions of her victim in relation to the sex tape.
He told the court: ''Mr Morgan played a significant part in humiliating and debasing Ms Contostavlos's reputation, clearly for financial gain.''
Sarah Asbrey, senior district crown prosecutor for the Crown Prosecution Service in the East of England, said after the hearing: ''It was clear from the evidence that Ms Contostavlos held a grudge against Mr Morgan for previous comments he had made about her on his blog including a link to her sex tape.
''When she saw him at the festival there was an argument between them, which resulted in her assaulting Mr Morgan. The outcome of this case shows that no-one is above the law and each case will be dealt with on its own merits.''
On Monday Contostavlos's trial over drugs allegations collapsed at Southwark Crown Court.
The singer was accused of boasting that she could ''sort out'' cocaine for Mr Mahmood and put him in touch with her rapper friend Mike GLC, who supplied the Class A drug.
She vehemently denied brokering the deal, which was exposed in the Sun on Sunday newspaper last June.
Mahmood was suspended by the paper after the trial was halted because of his evidence.