After finding fame alongside Ant McPartin and Declan Donnelly on SM:tv Live and spin-off music show CD:UK, Cat became a household name in the US, fronting shows such as So You Think You Can Dance? and This Time Next Year.
Lorraine, 61, will enjoy a much needed break over Easter week, with Cat taking over the reigns next week.
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Following the announcement, Cat said: “Lorraine has kindly entrusted me with her show while she has a break over Easter.
“I’m so happy to be back at ITV for the coming week and looking forward to meeting some people I’ve wanted to interview for sometime and also welcoming some old friends on air.”
One person confirmed to appear on the morning show next week is Louise Redknapp, who starred alongside Cat on SM:tv Live sketch Cat The Dog.
Stacey Solomon, singer Tom Odell and actress Melanie Hill are also booked in for chats with Cat during the week.
Good Morning Britain host and Strictly Come Dancing star Ranvir Singh will host the show for the second week of Lorraine’s break from 12 April.
Lorraine editor Victoria Kennedy said of Cat’s signing: “Next week the lovely Cat Deeley will take to the helm of Lorraine, providing viewers at home with much-needed Easter enjoyment.
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“As a huge fan of SMTV, I’m more than just a bit delighted. And of course we look forward to welcoming Ranvir back too. We’ve got a great lineup of Easter guests joining us.”
Cat’s pal Ant recently announced he almost “passed out” during the filming of a prank on her for Saturday Night Takeaway.
She was led to believe she was filming for an episode of CBeebies Bedtime Stories but Ant and Dec, both 45, were up to no good as usual as they caused plenty of mishaps on the set.
As Cat read a story to the camera, Ant dressed up a koala bear and caused his pal to keep stopping as he caused problems.
In their final surprise, a huge fire engulfed the set which left Cat terrified, and as the koala bear appeared to be trapped, she went in to save him.
“That was closest I have ever been to passing out in one of these suits,” he told her after filming. Clearly still fuming she was pranked, Cat joked: “Really? Oh, well that gives me a little bit of joy.”
Lorraine airs weekdays at 9am on ITV.