Tulisa Contostavlos stuck her middle finger up at ex-boyfriend Justin Edwards as she performed at the Barclaycard Wireless festival.
The N-Dubz singer and X Factor judge, 23, vented her emotions towards the rapper and MC, who has spoken of receiving death threats after he allegedly posted the infamous sex tape he filmed of them online.
Before she sang her cover of David Guetta's hit Titanium on the main stage, she said: "This song is dedicated to my ex. I'm still standing!"
Contostavlos - who also performed her single Young - showed off her figure in a low-cut bra top, star-print miniskirt and white jacket.
Around 33,000 revellers attended the sold-out outdoor gig at London's Hyde Park and spirits stayed high despite the brief rain showers to watch Nicki Minaj, Example, Professor Green, Wiz Khalifa and Rita Ora on the main stage.
Trinidadian singer Minaj, wearing a neon outfit with gold boots, was accompanied by topless male dancers as she performed hits like Super Bass, Starships and Beez In The Trap.
Canadian rapper Drake was joined by special guest Minaj as he closed the second day of the music festival, which also saw acts like Labrinth, Nero and Chiddy Bang perform.
"London is like my second home," he told the screaming crowd.
Rihanna, who closed BBC's Radio 1 Hackney Weekend a fortnight ago, is set to headline the closing night (July 8), and there is speculation that she may be joined by her ex-boyfriend Drake on their hit Take Care.
Jessie J, Calvin Harris and Rizzle Kicks will also be performing.