The wife of Wayne Rooney says she spent five months working out who was giving out information from her personal Instagram account.
She claims she worked out it was Rebekah's account by blocking everyone else's account apart from hers.
Rebekah - the wife of Jamie Vardy - has denied the allegation.
Both Wayne and Jamie have played together for the England football team.
Posting on Twitter, Coleen claimed that someone she trusted to follow her on her personal Instagram account has been leaking stories to the Sun newspaper for several years.
"After a long time of trying to figure out who it could be, for various reasons, I had a suspicion."
In order to try to prove it, she came up with a plan in which she blocked everyone from viewing her Instagram stories apart from one account.
After that, she posted various false stories on to her account to see if they ended up in the newspaper - which she says they did.
The stories Coleen mentioned were about gender selection in Mexico, being excited to go on Strictly Come Dancing and one about a flooded basement.
"It's been tough keeping it to myself and not making any comment at all, especially when the stories have been leaked; however, I had to. Now I know for certain which account/individual it's come from.
"I have saved and screenshotted all the original stories which clearly show just one person has viewed them.
"It's... Rebekah Vardy's account."
Coleen's post on Twitter had more than 12,000 retweets and 42,000 likes within an hour of it being uploaded.
Rebekah Vardy has responded to the claims in a message back to Coleen.
She denied it was her and said she wishes Coleen had spoken to her directly about her suspicion as she would have changed the password to her account.
"Over the years various people have had access to my Insta and just this week I found I was following people I didn't know or have never followed myself," she said.
"I'm not being funny but I don't need the money, what would I gain from selling stories on you?"
She added: "I'm disgusted that I'm even having to deny this. You should've called me the first time it happened."
Now, The BBC's Victoria Derbyshire programme has learned Rebekah has instructed lawyers to do a "forensic investigation" on her Instagram account to see who has had access to it and when.
The Sun newspaper said it did not want to comment on the claim, but it has removed one of the three stories Coleen flagged.