Zara Deniz Lackenby-Brown and Olivia Hawkins were shown in Monday's episode having a bitter argument about Tom Clare, one of the other contestants who they are both interested in.
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Hawkins, 27, had been coupled with Clare, but in a recoupling ceremony late arrival Lackenby-Brown, 25, got together with him instead.
It prompted some bad feeling between them, but when Hawkins pulled Clare for a private chat about the situation and Lackenby-Brown demanded to know what she had said, viewers were shocked at how quickly things escalated.
Hawkins smirked at some of the other contestants as she told Lackenby-Brown that her chat with Clare was private, and accused her rival of playing games.
But as Lackenby-Brown explained she saw a future with Clare, she asked Hawkins: "Why do you think I'm in here to p*** you off? I'm in here for myself.
"Do you think I've flown 11 hours from England to p*** you off?"
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The row lead viewers to believe that there was a huge back story between the pair that they knew nothing about - and some savvy fans had already spotted them having commented on each other's social media posts as if they knew each other years ago.
One viewer tweeted: "Sorry we NEED to know how Olivia and Zara knew each other before being in the villa because this beef is not making any sense."
Someone else agreed: "WHAT is the full tea between Zara and Olivia because this can’t be coming out of no where WHAT DO WE NOT KNOW!!!!"
Another viewer speculated: "this beef is so deeper than this someone needs to SPILL what’s happened w them on the outside."
It became a popular opinion with viewers, as one person tweeted: "Olivia dislikes Zara for reasons outside of the villa. Its so bait now. Zara hasnt done anything wrong inside the villa for olivia to go on like that."
Someone else agreed: "Olivia must have lost a man to Zara before because never in the history of Love Island has anyone been this prematurely b*** hurt…"
One viewer even went so far as to say about the row: "The love island producers KNOWING DAMN WELL they got Zara on that 11 hour flight just to p*** Olivia off."
Love Island continues tonight at 9pm on ITV2.