"Marvel's Agents of S.H.I.E.L.D." has commenced filming for its fourth season, which is set to premiere this fall on ABC. Because of its shooting schedule, some of the series' stars are likely to be absent from Comic-Con International: San Diego's "Agents of S.H.I.E.L.D." panel this weekend.

Star Ming-Na Wen confirmed the early start in a post to Twitter:

Day one. #AgentsofSHIELD Season 4 begins filming. Early calltime. The Cavalry is back on her horse, peeps!



Yeah, still hate waking so early- Ming-Na Wen (@MingNa) July 21, 2016

Plus, according to Latino Review, the Marvel NOW! version of Ghost Rider is set to appear in the third season of the series. The latest rumor follows a casting report, which included a description that sounded a lot like Robbie Reyes, the most recent incarnation of Ghost Rider.

Rumors of Ghost Rider's involvement in Season 4 of the series began when an "Agents of S.H.I.E.L.D."-themed SDCC train was revealed to be boasting a flaming chain -- the trademark weapon of Ghost Rider -- spread across it.

Perhaps we'll learn concrete information about Ghost Rider's presence on "Agents of S.H.I.E.L.D." at SDCC this weekend...

Starring Clark Gregg, Chloe Bennet and Ming-Na Wen, "Marvel's Agents of S.H.I.E.L.D." returns to ABC on Tuesday, September 20 at 10 pm EST.