SPOILER ALERT:The story includes plot details about the current Season 2 of Star Trek: Discovery on CBS All Access.

EXCLUSIVE: CBS All Access has big plans to expand the Trekverse, but Star Trek: Discovery is slimming down.

One of the biggest cast additions for the current second season of Discovery was Anson Mount, who came on board as Captain Christopher Pike of the USS Enterprise. He was joined by Rebecca Romijn, who was tapped to play another classic Star Trek character, Number One, a member of Pike’s crew.

Both are set to leave at the end of the season, we have learned.

According to sources close to the series, both Hell On Wheels alum Mount and Romijn had strictly one-year deals; the duo had been contracted only for Season 2 arcs as part of a plan to sync up Discovery with the original Star Trek lore by the end of the new series’ second season heading into Season 3.

As fans and viewers of the original series and subsequent big-screen efforts know, Mount’s Captain Pike was a captain of the USS Enterprise before James T. Kirk. Both Pike and Number One appeared in Gene Roddenberry’s original Star Trek series but fleetingly. Pike returned, with Bruce Greenwood portraying the character, in the 2009 and 2013 movies co-written by Alex Kurtzman.

Meanwhile, with production on Season 2 of Discovery now wrapped in Toronto, Mount was involved in an on-set physical altercation in August last year with a director while filming an episode.

The incident reportedly stemmed from a discussion of a scene, and Mount gesticulating and pointing, which was the action of the scene in question. In acting out that scene before the cameras were turned on, the actor’s hands made physical contact with the director.

Quickly after the incident occurred, it was reported by the production to CBS HR, which reviewed the matter. The department spoke to all parties involved, including Mount and the director, to determine what happened. Based on those discussions and the inquiry, the incident did not result in any disciplinary action against the actor.

Even before HR got involved, Mount apologized to the director and work on the episode continued. The incident is said to have zero to do with Mount leaving Discovery; one source close to the production told Deadline that “we would love to find a way to work with Anson again.”

No word yet on whether that will happen and how it could work as Discovery moves more into the traditional Trek timelines.

In January, Discovery co-creator, executive producer and showrunner Kurtzman talked with Deadline about Pike’s “mythological place in canon” despite being seen only once in the original series — in the two-episode story called The Menagerie that aired in November 1966.

“This season we get inside his character in a way that we we didn’t get to do in the films,” he said. “And the fact that we will synchronize with canon by the end of this season, that means we may see shades of where we all know Pike will end up.”

This is a reference to Pike’s grim fate — in the 1960s series, the character is portrayed as paralyzed, disfigured and mute. (In the Kelvin timeline, shown in the J.J. Abrams-directed Star Trek films, Pike dies at the hands of the superhuman known as Khan.)

Geoff Boucher contributed to this report.