Dewberry beat her competitor Ruth Badger to win a job with Sugar in the show's second series.
Speaking at the launch of the new series, Sugar explained that he might not have made the right decision.
"[Picking Michelle over Ruth] is the only one where you could say that there is some regret," he said. "And the regrets really were very much that she decided that what my company had to offer was not for her. The reason Ruth wasn't chosen is another private issue."
However, Sugar explained that he is largely pleased with the previous winners of The Apprentice.
"I think if you go back and look at Tim Campbell, for example, he worked for me for two years," he said. "We'll skip the lady that we spoke of earlier on, and move on to Simon Ambrose who worked for me for two years. Lee [McQueen] worked for me for two years and Yasmina [Siadatan] is working for me now. They've done a great apprenticeship for me."
The new series of The Apprentice begins on Wednesday, October 6 at 9pm on BBC One.