Sen. John McCain (R-Ariz.) snagged a reelection endorsement from his top primary opponent from the 2008 presidential campaign.

Former Massachusetts Gov. Mitt Romney (R) issued a statement on Tuesday backing McCain for reelection amidst a conservative primary challenge from former Rep. J.D. Hayworth (R-Ariz.).

"For years, I've been an admirer of John McCain. Then we became competitors. Today, I'm proud to call him my friend," Romney said in a statement. " Not only am I proud to call him a friend, but as an American I am constantly reassured by Senator McCain's continued involvement in the affairs of our nation, and I am honored to support him.”

The endorsement can be seen as a strong sign that Romney continues to collect political chits as he prepares for a possible second White House bid in 2012. The endorsement also lends McCain some conservative cachet in the potentially bruising battle against Hayworth.

“Governor Romney is among the brightest and most dynamic leaders in our Party, and I am proud to have his support,” McCain said in response to the endorsement. “I look forward to working with him to advance our shared vision for a stronger, safer and more prosperous America.”