Executive producers and showrunners Aaron Harberts and Gretchen J. Berg are exiting “Star Trek: Discovery,” Variety has confirmed. Executive producer and co-creator Alex Kurtzman will take over showrunner duties for season two.

“We’ve made some producer changes at ‘Star Trek: Discovery,'” a CBS Television Studios spokesperson said in a statement. “The series continues under the creative vision and leadership of executive producer and co-creator Alex Kurtzman. ‘Discovery’ remains on course for season two in 2019 with new and continuing stories that build on its successful premiere season.”

Harberts and Berg’s exit marks the second showrunner departure for “Discovery,” as the CBS All Access drama heads into its second season. Co-creator and original showrunner Bryan Fuller exited the series months before its premiere last year following multiple delays. At the time, Harberts and Berg — longtime writing partners who had worked frequently with Fuller and were staff writers on the pilot — took over as showrunners, with Kurtzman taking on a more involved role in the big-budget drama.

Sources tell Variety that tension had been building in the writers room as work continued on season two, which remains set to premiere in 2019.

Production is well underway on “Discovery” season two, with sources indicating that five episodes are nearly complete. The show now heads into a planned production hiatus as Kurtzman, whose company Secret Hideout produces the CBS Television Studios drama, prepares to take over day-to-day management of the show. Akiva Goldsman, who had come aboard “Discovery” as executive producer for season one following Fuller’s departure, is not returning tot he show for season two.

The Hollywood Reporter first reported on the showrunner change.