The Glasgow singer is set to take to the stage at Murrayfield tonight with the former Take That star as part of his UK tour.
Michelle had previously interviewed the Angels hitmaker on her BBC Radio Scotland show when he proposed the duet, The Scottish Sun reports.
However, ahead of the gig, the 45-year-old admitted that the thought of singing to 70,000 people has brought on the nerves.
More so than her performance for the Pope.
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She said: “My happy place is when I sing, so the singing part is not the problem, the nervous part is singing to Robbie Williams in front of 70,000 people.
“When we did the Pope’s visit in Bellahouston, it was 80,000 – but singing for a bunch of cardinals and a Pope was slightly different from singing for Robbie Williams.”
McManus, who rose to fame after winning the final series of Pop Idol in 2003, and Williams have known each other since the early 2000s.
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Robbie later agreed to be part of Michelle’s 2023 documentary about talent show winners.
Whilst it remains a mystery what the pair will perform together, Michelle did reveal that her outfit is adorned with 40,000 Swarovski crystals.
She added: “I’m never going to take it off. It is one of the most beautiful things I have ever had on my body.
“You will not need to worry about seeing me from the stage, from the colour of my hair and the amount of crystals.”
