Her shock discovery six weeks ago led to the announcement that they were splitting up after 14 years of marriage.
It comes after we told last week how news presenter Eamonn, 64, has become close friends with a blonde divorcee in her 40s — who works as a relationship counsellor.
The Belfast-born anchor has been on outings with her and showered her with gifts.
It is understood the messages Loose Women host Ruth, 64, stumbled across were to and from the same woman.
Meanwhile, a picture has emerged of Eamonn on a day at a safari park in February where the woman is thought to be seen through the rear window of a vehicle.
A source said: “Ruth was completely taken by surprise when she saw the messages.
“She had no idea what had been going on between them. She was devastated.
“Not only was she very upset but she was also angry.”
Eamonn has moved out of their marital home in Surrey.
Meanwhile, Ruth is taking an extended break from ITV’s Loose Women as she struggles to deal with their marriage breakdown.
Over the past year, Eamonn has treated the woman to a Beyoncé concert, a Center Parcs visit and tickets to see his beloved Manchester United at Old Trafford.
They became friends after she made a comment on one of his social media posts and they immediately struck up a rapport.
Eamonn has also endorsed a charity linked to her counselling work, helping to host a fundraising event free of charge.
Last week, a source close to the Northern Irish star said: “She works for a charity Eamonn is involved with from time to time.”
Eamonn and Ruth announced on May 25 that they had split and were divorcing — as revealed exclusively by The Sun on Sunday.
Ruth has confided there is “no way back” for their marriage.
MARRIAGE BREAKDOWN
Cracks had become apparent after the pair, who have son Jack, 22, were not photographed together for around two years.
It was reported GB News host Eamonn’s health issues, including crippling back pain, had placed a strain on their relationship.
But pals of Ruth say she has been “upset” at the claims that was the reason for their split.
Eamonn lavished his wife with praise for her “amazing” support after he suffered a fall down stairs of their home in November 2022.
And last month she was a visitor when he had a spell in hospital following another medical scare.
Earlier this year, Eamonn detailed his ongoing “epidemic of pain” which has left him relying on a walking stick and wheelchair.
And he said the “harsh reality” could be he may never be able to walk unassisted again.
Last year he was unable to attend his mother Josie’s funeral due to his health.
She had no idea what had been going on between them. She was devastated
Source
Discussing his woes, he said: “It’s as if somebody up there is playing with my life.
“In the past year I’ve had an operation on my back which went wrong and has confined me to a wheelchair. I’ve fallen and broken my shoulder. Honestly, you could not make it up.”
In 2018, Eamonn was hit by a bout of shingles — a viral infection that causes a painful rash.
He reckoned it was brought on by a stressful tax row with HMRC over whether he was classed as staff or a freelancer while a presenter at This Morning.
Ruth publicly addressed their split for the first time on Thursday when she thanked fans for their messages of support during a live stint on shopping channel QVC.
Prior to news of their separation, in a discussion on Loose Women last month, Ruth confessed it would not bother her as much if her husband left her for a 25-year-old.
She said: “The worst thing is if he went off with someone the same age. That’s my worst fear.”
Eamonn and Ruth jointly presented ITV’s flagship show This Morning until 2021.
He now hosts GB News with Isabel Webster.
The Sun on Sunday approached both Eamonn and Ruth for comment.