The presenter and her husband Eamonn Holmes usually host Friday's edition of the programme each week but there was no sign of Ruth today.
At the start of this morning's show, Eamonn told viewers: "If you're thinking Ruth looks very well today, it's Rochelle."
Rochelle said: "You say the same thing every time and I tell you not to!"
Eamonn added: "Ruthie's got other things to do today so she can't be here today but Rochelle and I are pairing up!"
Former Saturdays singer Rochelle then joked she was the perfect choice to fill in for Ruth because they could keep the This Morning mugs in place for her.
She said: "I always say they don't have to change the mugs, the cups can stay the same - E and R. It works, we like it.
"I'm Mrs Holmes for the day!"
Viewers were baffled by Rochelle's appearance and asked where Ruth is on Twitter.
One person wrote: "#ThisMorning Omg where is Ruth," while another said: "Has Ruth got the Coronavirus?"
A third added: "#ThisMorning no Ruth today?"
#ThisMorning Omg where is Ruth
— Joe Mackenzie (@JoeMackenzie16) February 28, 2020
Has Ruth got the Coronavirus? #ThisMorning
— HeadSpinRooney (@RSMN_10) February 28, 2020
#ThisMorning no Ruth today?
— travelprincess99 (@ruth_clark) February 28, 2020
— Juliette Julz ⫩ (@julesywoolsey) February 28, 2020
Where’s Ruth? #ThisMorning
— ✯ ✯ (@EatPieKillDemon) February 28, 2020
Ruth and Eamonn recently celebrated their son Jack's 18th birthday and both paid tribute to their son on Instagram.
Ruth shared a video on Instagram of a glam dinner table set out with silverware, giant '18' balloons and plenty of glitter.
Ruthie's got other things to do today but she can't be here today but Rochelle and I are pairing up!
She captioned the post: "The scene is set! Traditional birthday breakfast table for Jack’s 18th!!! Our baby’s all grown up!!"
Eamonn, 60, shared a rare photo of their son Jack, who is rarely seen in the spotlight.
Sharing a beaming father son photo to his some 588,000 followers, Eamonn gushed over how proud he was of his youngest child.
He wrote: "My Baby Son becomes 18 today , all grown up and at least 6 inches taller than his old Dad.
"Couldn't be more proud of the young man he has become. Many Happy Returns Jack."
Eamonn has three further children with his first wife, Gabrielle Holmes - Declan, 31, Rebecca, 29, and Niall, 27.
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