Late Monday night, as Americans were preparing to ring in the new year, Defense Secretary James Mattis was having a very different sort of evening. After decades of service, the former Marine general relinquished authority over the Pentagon to his former deputy secretary and current acting defense secretary, Patrick Shanahan.

According to the Department of Defense, the turnover was completed at 11:59 local time on Monday night, placing Shanahan in the role just as a tumultuous year for the Trump administration came to a close.

Although President Trump seemed to revel in Mattis’ reputation as a war-fighter and the nickname “Mad Dog” early on, rumors of the relationship between the two souring permeated throughout Washington D.C. for months prior to Mattis’ resignation. Ultimately, it appears the president’s decision to withdraw troops from Syria and Afghanistan solidified Mattis’ decision to leave, though the language contained within his highly publicized resignation letter suggests the two had failed to find much common ground on anything during their nearly two years spent working together.

Prior to his departure, Mattis released one last memo addressed to all Defense Department staff in which he tempered the rhetoric contained within his resignation letter, acknowledging the challenging situation and emphasizing that America’s war-fighting apparatus will remain as strong and capable as ever under the forthcoming leadership.