John Barrowman, who plays the villain Malcolm Merlyn on "Arrow" and is set to reprise the role for the show's upcoming fifth season, has been confirmed to be a series regular on all of the other DC shows on the CW Network such as "The Flash," "Legends of Tomorrow" and "Supergirl."

According to a report from TV Line, this will allow the villain to appear and cause trouble on any of these shows while still staying on "Arrow" as one of the main villains fighting against Oliver Queen aka the Green Arrow (Stephen Amell).

It is further confirmed that this refers to a more regular appearance compared to the one or two episode guest appearances that usually happens when the shows have a cross-over event. Some guest appearances in the past include Stephen Amell appearing on "The Flash" and Barry Allen aka the Flash (Grant Gustin) on "Supergirl."

Screen Rant points out that a better example of an actor being upgraded to series regular on more than one show is that of Wentworth Miller, who plays the villain-turned-hero Captain Cold. Captain Cold is primarily an anti-hero on "The Flash" but is also a main cast member of "Legends of Tomorrow."

The report also reiterates a statement that producer Greg Berlanti made back in May, a statement that at the time referred to Wentworth Miller but also applies to the situation regarding Barrowman. 

"What it really emulates to us is the comic books themselves, where there really are a cast of characters. In success, we hope to continue with other characters finding their way across all the shows," explained Berlanti at the time, confirming that the studios are attempting to build a unified cinematic universe on the CW network. 

Fans of the original comic books will point out that this will make the shows closely resemble the structure of the comic books where characters from one comic book line appear on others, giving audiences the sense that they are invested in a much larger world.

"Arrow," "The Flash," "Legends of Tomorrow" and "Supergirl" are all set to premiere this October.