New Jersey Gov. Chris Christie, right, hands the microphone to Republican presidential candidate, former Massachusetts Gov. Mitt Romney during a campaign stop at Bun's Restaurant and Bakery, Wednesday, Oct. 10, 2012, in Delaware, Ohio. (AP Photo/ Evan Vucci)

New Jersey Gov. Chris Christie (R) is getting some fundraising help from the man who once called him "pufferfish," made fun of his weight and passed him over for the vice-presidential spot on the Republican national ticket.

According to CNN, two-time presidential hopeful Mitt Romney (R) will appear at a September fundraiser with Christie, chairman of the Republican Governors Association and a possible 2016 presidential contender.

The event is being promoted as a birthday celebration for Christie, who will turn 52 on Sept. 6. According to an invitation to the event, attendees can pay $150 for general admission, $5,000 to attend a private reception or $25,000 to attend a roundtable.

The Christie fundraiser is the latest in a series of national appearances for Romney, who has been back in the spotlight while campaigning on behalf of GOP candidates this year. A recent CNN/ORC International poll found that if the 2012 election had been held last week, Romney would have defeated President Barack Obama.