If you can't remember the last time two African-Americans simultaneously served in the U.S. Senate, it's because it has never happened. That's all about to change now that William “Mo” Cowan is headed to Washington, where he will join Sen. Tim Scott (R-South Carolina).

Massachusetts Gov. Deval Patrick on Wednesday will name Cowan, his former chief of staff and legal counsel, to fill the seat vacated by Sen. John Kerry, who was confirmed Tuesday as the next secretary of state. He served as Patrick's chief of staff from January 2011 to November 2012 and returned to practice law in the private sector this month.

Massachusetts hasn't had an African-American in the Senate since Edward Brooke, a Republican who held the seat from 1966 to 1978.

The commonwealth will hold a primary election on April 30 and the general election on June 25.

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(Photo: AP Photo/Massachusetts Governor's Office, File)