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Mo Cowan to fill John Kerry's Senate vacancy

Photo: Massachusetts Governor's Office

Former Rep. Barney Frank (D) clearly wanted the gig, but John Kerry's Senate vacancy is instead going to an unexpected choice.

Massachusetts Gov. Deval Patrick (D) will appoint his former chief of staff, William "Mo" Cowan, to be the interim pick to fill the state's vacated U.S. Senate seat at 11:00 am ET Wednesday, a top Democratic aide and a Massachusetts political operative confirm to NBC News.

Cowan, who is African American, will be Massachusetts' second black U.S. Senator. The first was Republican Ed Brooke, who served from 1967 to 1978.

Cowan is not an especially well-known figure outside the Bay State, but the AP reported, "Cowan, 43, became chief-of-staff to Patrick in 2010 after first serving as chief legal counsel during the Democratic governor's first term. He stepped down as Patrick's top aide in December, though he remained on a senior adviser through the filing last week of the governor's state budget request."

There is a fair amount of historical significance associated with the choice. Once Cowan takes office, he'll be only the eighth African American to serve in the U.S. Senate, and it will be the first time in American history that two African-American senators served at the same time -- South Carolina's Tim Scott (R) was appointed to fill Jim DeMint's vacancy earlier this month.

Moreover, with Sen. Elizabeth Warren (D) having been elected a few months ago, this will also be the first time in American history that a state's Senate delegation has been made up of one woman and one African American. While we're at it, let's also note that Massachusetts will now be the first state to ever be represented by an African-American governor and an African-American senator at the same time.

Looking ahead, Cowan will serve though the June special election, and will not seek a full term of his own. That said, the Democratic race is poised to get a little larger -- Rep. Stephen Lynch (D-Mass.) will launch his campaign in Boston tomorrow, and will take on Rep. Edward Markey (D-Mass.) in a primary.

It's worth noting that Lynch is the only Democrat in New England who voted with Republicans to kill health care reform, supported the Iraq war, and opposes abortion rights, suggesting he may struggle to win his party's nod.

On the other side of the aisle, Republican Scott Brown, who just lost his Senate seat three months ago, is reportedly "leaning strongly" toward running again, despite his recent public rejection.