Whelan, who was previously art editor of the magazine for 10 years, replaces Maria Trkulja, who left earlier this month following editorial differences with owner Eduardo Sanchez Junco after the long-running and costly court case with Catherine Zeta-Jones and her husband Michael Douglas.
Her appointment comes amid a reshuffle at the magazine, which includes three internal promotions, led by Susan Rosznyai, who becomes editor at large; Linda Newman is appointed assistant editor (commissioning); and Ruth Sullivan moves up to assistant editor (copy and production).
"I am thrilled to be coming back to Hello! and looking forward to working with everyone there. The visual side of Hello is so important, as it's always been very much a picture-led magazine and that is where my expertise lies," Whelan said.
Another former editor of the title, Maggie Koumi, has been appointed consultant editor with responsibility for special projects.
Hello! published pictures of Zeta-Jones and Douglas after the couple had already sold the rights to the photos to rival magazine OK!. Hello! was cleared on nine out of 13 counts brought against it and the judge refused to rule on the claim that the Douglases' privacy had been breached.
However, he found that Hello! had breached the laws of commercial confidence and the magazine will have to pay damages to the couple and OK! to be decided at a later date.
Hello! had an ABC circulation of 546,952 in the last set of figures for July-December 2002 period. This was up 5.6% on the previous period, and a year-on-year increase of 3.8%. However, the magazine sits behind OK!, its rival in the mature celebrity magazine sector, which has a circulation of 632,791.
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