Prosser, 28, spent his first five NHL seasons with the Wild; he signed a one-year, two-way contract with the Blues on July 22.
"To get the news that I'm coming back and to get that Minnesota Wild jersey back on, it's been a wild day," Prosser said.
In 53 regular-season games with the Wild last season, Prosser had two goals, six assists and a plus-2 rating. In 10 Stanley Cup Playoff games he had a plus-2 rating and seven shots on goal.
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