Donald Trump believed he'd be done running for president by October 2015, and planned to endorse New Jersey Gov. Chris Christie, CNN reported Monday.

In a new book about the 2016 presidential election, a Christie adviser told reporters from the network that Trump's original plan was to drop out of the race in October 2015. He had told Christie that he would give him his endorsement when he did withdraw from the race.

Instead, Christie would become one of Trump's first major backers from the GOP's political class and ended up being one of the new president's top advisers.

According to the report, Trump and Christie were both working against Florida Sen. Marco Rubio during the Republican primary. Rubio would end up being ripped mercilessly by Christie for repeating a talking point during a debate and engaged in some memorable back-and-forths with Trump, most notably discussing the size of Trump's hands.

Christie and Trump clashed on a few occasions early in 2016, such as when Christie criticized Trump as an unserious candidate and Trump said Christie was well aware of the Bridgegate scandal before it broke.

The wounds appeared to be mended when Christie was appointed as the leader of Trump's presidential transition team, but recently Christie has fallen out of favor with Trump again. He was replaced by Vice President-elect Pence as the leader of the transition last week after Christie's involvement in the Bridgegate scandal once again made headlines.