The pair, who won the latest series in the summer, have parted ways after six months together.
In a statement on Instagram, Dani told fans: "Jack & I have sadly decided to part ways. It's been an incredible 6 months, and we will always have a place in our hearts for each other, but sadly we've come to the realisation that it's not meant to be long term.
"We both plan to stay friends. I hope you'll all understand. Love Dani x"
A source had claimed to The Sun newspaper earlier that the pair's relationship became "strained" shortly after leaving the villa.
"They came out to a whirlwind of publicity and after a while, things started to get to them and the cracks appeared," the insider alleged. "They are both incredibly busy and they have decided to call time on their romance."
The news comes as the pair filmed for their own reality show, Jack and Dani: Life After Love Island. Due to air on ITVBe, it's not yet been announced if the series will go ahead.
Jack had recently insisted that - while there had indeed been "bickering" - the pair were very much still going strong.
He told The Sun while filming for the show with Dani: “We do have arguments but people can’t think the world is going to end because we’ve had a row. It’s a normal thing having an argument.
“Filming the show wasn’t easy. It was tough, it was intense – you’re on camera most days of the week all day long.
“We had bickers during filming just like any other couple. I got emotional with Dani doing it; I even had a couple of tear ups. But Dani and I got through it.”
Love Island will be back in 2019 on ITV2.