Batman: Yes, Bruce Wayne Has A Sister - But Only In One Story

"Pennyworth," later retitled to the more SEO-friendly "Pennyworth: The Origin of Batman's Butler," showcases what Alfred Pennyworth (Jack Bannon) was up to before he sewed up Batman's wounds. He's a former British soldier who finds himself in the middle of various political machinations, which eventually cause him to run into Thomas Wayne (Ben Aldridge) and Martha Kane (Emma Paetz). To what was surely many people's surprise, the couple has a daughter — Samantha Wayne (Jayda Eyles). 

Bruce Wayne never ends up existing within the show's three seasons. Instead, audiences get Samantha, who has never appeared in a piece of Batman media before. She's the future long-lost-sister of Bruce, and if "Pennyworth" were allowed to continue, there's a chance the show would've explained why Samantha never became part of the traditional Batman mythos. Given the show's premature cancelation, it's unlikely Samantha will ever rise to the status of appearing in other Batman properties, but it is important to note that this isn't the first time Bruce has been given a sibling.

"Pennyworth," like other DC shows that ended prematurely in the vein of "Titans" and "Doom Patrol," had plenty of fans and easily could've gone on for a while. If it had, there's a chance Samantha Wayne could've developed into a character with a stronger mythos tied to her eventual brother, Bruce. While this may be the only iteration of her in Batman media, Bruce Wayne has had a brother before, and there's a chance Samantha could've followed in Thomas Wayne Jr.'s footsteps.

In the DC multiverse, there are several realities where Bruce Wayne has a brother. The first version readers were introduced to involved Thomas Wayne Jr. being sent away to Willowood Asylum. Upon reaching adulthood, he escaped and became the Boomerang Killer. In a different reality featured in the "Crisis on Infinite Earths" event, Thomas is established as Owlman, a dark counterpart to Batman who lords over Gotham with an iron fist. Thomas also factored into the "Court of Owls" storyline with Lincoln March, who claimed to be the assumed-dead brother of Bruce Wayne.

Regardless of continuity and reality, Thomas Wayne Jr. is generally portrayed as a dark mirror of what could've happened to Bruce. It's interesting "Pennyworth" decided to turn Bruce's sibling into a girl, and if the show were allowed to continue, perhaps she would've shown some villainous tendencies down the line.