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Steele, who previously played guitar with the band in the mid-'90s, has been given the job following Gray's death last May.
A statement on the band's website read: "Donnie was in the band at the very beginning, and rather than get an outsider, we thought it would be a fitting tribute to Paul to play with someone from within the family.
"Donnie was great friends with Paul and we can't think of a better way to celebrate his memory than with someone who was there with us at the very beginning."
It continued: "The eight of us are looking forward to being onstage again and honouring Paul's legacy with our families in Europe and Brazil this summer."
