"She has been showing (the ring) off to friends and family and is very happy," an insider told US Weekly. "She wants to… enjoy (it) and celebrate for a bit longer."
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There was speculation that Tim had popped the question when Kelly was seen wearing a large diamond ring in a video on a friend's Instagram account.
This will be the Destiny's Child star's first marriage. She was previously engaged to footballer Roy Williams; they split up in January 2005, just two months before their wedding.
"I was too young for marriage," the British X Factor judge told Cosmopolitan UK in 2011. "But sometimes you fall down and you learn from it."
Kelly posted a picture on Instagram where she is reportedly wearing her engagement ring
She added that she would be "ready for marriage when the right time comes".
The newly-engaged couple have not yet announced any details about their upcoming nuptials.