Former Sen. Scott Brown said Friday that he won't make a bid this year to return to Capitol Hill.

The Republican from Massachusetts announced that "I will not be a candidate for the United States Senate in the upcoming special election."

That special election will be held on June 25, with the winner filling the final eighteen months of the term of longtime Democratic Sen. John Kerry, stepped down from the Senate Friday and was sworn in as secretary of state.

In January 2010, then state lawmaker Brown upset Democratic candidate Martha Coakley, the state's attorney general, in a special election to fill the final two years of the term of longtime Democratic Sen. Ted Kennedy, who died the previous summer.

Brown won the special election by five points over Coakley, but lost his re-election bid in November to Democratic challenger Elizabeth Warren by eight points. Around 2.3 million voters cast ballots in the 2010 special election, and nearly 3.2 million voted in last November's general election.

Whoever wins the June special election would then have to run again in 2014 for a full six-year term in office. For Brown that would have meant running for four Senate elections in less than five years. And that appears to be a factor in Brown's decision.

"Over these past few weeks I have given serious thought about the possibility of running again, as events have created another vacancy requiring another special election. I have received a lot of encouragement from friends and supporters to become a candidate, and my competitive instincts were leading in the same direction," said Brown.

But he added that "even so, I was not at all certain that a third Senate campaign in less than four years, and the prospect of returning to a Congress even more partisan than the one I left, was really the best way for me to continue in public service at this time."

Thursday Democratic Rep. Stephen Lynch announced his bid for Kerry's Senate seat, becoming the second candidate to jump into the special election. Lynch joins fellow Democratic Rep. Ed Markey, the longest serving member of the Bay State's congressional delegation. The Democratic primary will be held on April 30.

Lynch quickly reacted to Brown's decision, saying "I understand Scott Brown's decision. He has basically been campaigning non-stop for three years. It's perfectly understandable that he wouldn't want to undertake another campaign. I wish all the best to Scott and his family."

Brown was likely the Republicans best chance of flipping Kerry's seat to the GOP. With Brown not running, the spotlight could turn to former Republican Gov. William Weld, who recently moved back to the Bay State, or former GOP Lt. Gov. Kerry Healey, says a Republican strategist who lives in Boston and who asked to remain anonymous to speak more freely.

Brown's decision was first reported earlier Friday by the Boston Herald, and three Republican sources confirmed the news to CNN.

Wednesday Democratic Gov. Deval Patrick announced that a trusted former aide was his choice to serve as an interim replacement for Kerry. Patrick named William "Mo" Cowan, his former chief of staff, as senator.

Cowan, who will serve through the June special election, will become the second African-American in the U.S. Senate, alongside Republican Tim Scott of South Carolina. Scott, who was just elected in November to a second term as a congressman, was named last month to succeed Sen. Jim DeMint, who stepped down from his seat.