WASHINGTON and SANTIAGO, Chile — Defense Secretary Jim Mattis said Thursday that his senior military assistant, Navy Vice Adm. Craig Faller, will be nominated to serve as the next head of U.S. Southern Command.

Mattis made the statement to members of a Chilean government delegation before attending a signing ceremony for an agreement on cyber cooperation with Chilean Defense Minister Alberto Espina.

The nomination was expected to be publicly announced later Thursday in Washington, and still requires confirmation by the Senate. If confirmed, Faller would become a four-star admiral, a rapid rise for someone who had only two-stars in January of last year.

Faller studied engineering at the Naval Academy and worked in nuclear specialties early in his career. Later, as a commanding officer, he deployed repeatedly the Middle East, leading combat forces supporting U.S. military operations in the Persian Gulf, and in Iraq and Afghanistan. Before taking the job with Mattis, he worked as the Navy’s point man for legislative affairs

Mattis selected Faller as his military assistant just days after being sworn in as secretary, continuing an existing relationship between the two. While assigned to Central Command, Faller was investigated by the Navy Inspector General over allegations he breached military ethics rules when, as a carrier strike group commander in 2011, he was offered and accepted a luxury hotel suite in Malaysia.

The Navy determined Faller’s missteps were mitigated because he accepted the room upgrade to accommodate several members of his staff. It was Mattis, as Faller’s boss when the investigation was complete, who elected to forego disciplining the admiral.