The pair called time on their relationship at the end of November, after around three months together.
And, despite the Love Island star keeping quiet about the reason behind his break up from the Made In Chelsea beauty, reports claim he was unfaithful with another reality TV star.
“Steph thinks that Jonny was cheating on her and she’s convinced it was with a girl, who she’s met several times, on the reality TV circuit from a really famous TV show,” an insider reportedly told The Sun.
[Instagram/ Stephanie Pratt]
“She’s heard a lot of rumours from fans and friends about the girl since she and Jonny broke up.
“Steph doesn’t know what to think – her head is in a weird place and she’s hearing a lot of things from a lot of people.
“She’s worked herself up into a state where she doesn’t know who to believe but she’s convinced something was going on between Jonny and this female reality star.”
Love Island winners Kem Cetinay and Amber Davies split as there work commitments got in the way of their relationship [Getty ]
Jonny has kept quiet following their split but, during an interview on Fubar Radio, admitted he felt people were trying to ‘sting him’.
But, a source close to Steph – who has since been linked to Pete Wicks – claims the rumours have made her doubt their entire relationship.
“She’s thinking back and wondering why she didn’t meet his friends and he was so keen to meet her ‘celebrity’ mates,” they continued to the publication.
“Steph didn’t meet his family, yet he really wanted to come to LA with her in October to meet Heidi and Spencer and her new nephew Gunnar.
“He’d always stay at her flat, and want to party with her friends. Now she’s wondering why she never saw any of his life or people he was close to.”
Jonny confirmed their relationship was over last month, sharing an exclusive statement with OK! Online.
“Jonny Mitchell and Stephanie Pratt have ended their relationship,” it read.
“Jonny has fond memories of the times they spent together and wishes Stephanie all the best of luck in the future.”
OK! Online has contacted reps for Stephanie and Jonny for a comment.