Gemma Collins accused Sinitta of being a 'rat' in the I'm A Celebrity All Stars' WhatsApp group, according to reports.
The spin-off show will return to screens on April 6, with an all-star line up of past campmates.
But tensions have already reached fever pitch before the launch, after Gemma, 45, is said to have accused Sinitta, 62, of betraying her by leaking stories to the press.
Sinitta was reportedly 'dumbfounded' and 'incredibly upset' by Gemma's suggestion, with the spat having now put a 'massive cloud' over the once 'jolly' group chat.
A TV insider told The Sun: 'All Stars hasn't even aired yet, but it's all been kicking off, Gemma is at the centre of this astonishing new spat.
'A few weeks back, out of nowhere, she dropped a message into the group WhatsApp chat accusing someone of leaking stories about her to the press. And before anyone could even tap out a reply, she accused Sinitta of being the rat.
Gemma Collins accused Sinitta of being a 'rat' in the I'm A Celebrity All Stars' WhatsApp group, according to reports
'It was like Wagatha Christie all over again. No one in the group could believe what they were reading. No one replied. Basically, it put a massive cloud over what had been a rather jolly group. Some of the celebs in the chat rallied to Sinitta because they felt it was unnecessary to make such an accusation in a group setting.'
The insider added Sinitta tried to approach Gemma at the All Stars launch at the Ham Yard hotel in London earlier this month to smooth over any tension.
However, they claimed the singer was 'taken back' after Gemma brushed over the accusations she had made and was 'was very nice to her face'.
They added: 'It left a bad taste in a lot of famous mouths because Gemma had caused all this tension, then just made out like it was nothing. Sinitta was obviously pleased it had been put to bed.'
The rest of the cast are now said to be worried Gemma could suddenly turn on them.
Daily Mail has contacted Gemma and Sinitta's representatives for comment.
Tensions have already reached fever pitch before the launch, after Gemma, 45, is said to have accused Sinitta, 62, of betraying her by leaking stories to the press
Gemma took part on I'm A Celebrity back in 2014. She famously quit the show just 72 hours.
Sinitta, meanwhile, entered the I'm A Celebrity... Get Me Out of Here! jungle 15 years ago in 2011.
The latest tension comes after it was revealed Adam Thomas fell into a fit of rage with footballer, Jimmy Bullard, during filming for the show.
The Waterloo Road star, 37, jetted to South Africa with his fellow All Stars including Scarlett Moffatt, Harry Redknapp and Gemma in September for the ITV show.
When asked how he found the experience, Ryan said: 'It was tough, there's no denying that and I feel like I had my moments in there, like we all did. I'm glad I did it, it's amazing to be back after 10 years.
'I got such imposter syndrome, it's a lot to take in and it was a lot to take in. It was an experience to say the least but I'm glad that I did it.'
The father-of-one was joined at a Q&A session hosted by Sam Thompson and Kemi Rogers at the Ham Yard Hotel but Jimmy, 47, was a no show as it's reported the pair no longer speak.
Sean Walsh tried to insist they were all still friends, but former Queen of the Jungle Scarlett Moffatt revealed none of them used the group WhatsApp anymore.
The Gogglebox star, 35, said: 'Let's not lie on this stage. I think naturally, in a social setting like that, you are drawn to certain people over others.
'That's just life, we did all get on. But, there were peaks and troughs wasn't there.'
