Charles Krupa/AP Photo

William "Mo" Cowan will temporarily fill the Senate seat being vacated by John Kerry, Massachusetts Gov. Deval Patrick announced this morning.

Cowan is Patrick's former chief of staff and will serve the Bay State in the Senate for almost five months, until a special election to fill out the rest of Kerry's term. Patrick also formally announced that the special election will take place June 25.

"I am proud and delighted to appoint Mo Cowan as interim U.S. senator from Massachusetts," Patrick said in a statement.

"Mo's service on the front lines in our efforts to manage through the worst economy in 80 years and build a better, stronger commonwealth for the next generation has earned him the respect and admiration of people throughout government," he said. "The people of the commonwealth have benefited from his wisdom and good judgment during his time in our office, and will again in the Senate."

Cowan was perhaps one of the less well-known candidates on the list of potential interim appointments to fill Kerry's seat upon his resignation. Vicki Kennedy, the wife of the late Sen. Ted Kennedy, who held the state's other seat, and former Rep. Barney Frank were also on the list of possible temporary replacements.

Cowan's appointment is historically significant in Massachusetts and nationwide. When Cowan takes office, it will be the first time in U.S. history that two black senators will be serving simultaneously in the Senate (South Carolina Sen. Tim Scott is the other.) Cowan will be the eighth ever African-American senator.

It will also mark the first time in Massachusetts history that there will not be at least one white male among the Senate delegation. Cowan will join Sen. Elizabeth Warren, who became the state's first female senator when she won her race in November.