"Smallville" began airing on The WB in 2001. It went along for the ride after The WB and UPN merged in 2006. It concluded its run as one of the longest-running American science fictions shows in history. In addition, it continued on in comic form.

The success of "Smallville" directly led to the current slew of DC series on The CW, as UPI.com notes. After several twists and developments, the franchise has become known as the 'Arrowverse'. And "Smallville" is to formally become part of the franchise it helped spawn.

Tom Welling to portray Clark Kent again

Welling starred on "Smallville" for the entirety of its run. According to MSN, he will play the role again for the upcoming 'Crisis on Infinite Earths' storyline. It is to be the same version of Clark Kent he played on "Smallville". Full details of his involvement haven't been announced. But at least in part, it should update fans on what happened to character after "Smallville" ended.

'Crisis on Infinite Earths' is based on an iconic plot from DC's comic books. It's including all series that currently make up the Arrowverse. They are "Arrow," "The Flash," "Supergirl," "Legends of Tomorrow," "Batwoman" and for the first time, "Black Lightning." The storyline allows for various cross-overs, making it an ideal if challenging plot for the franchise to take on.

A couple of other things about it should be noted. The story also led to the entire DC comic books universe to be re-booted. It also included the deaths of various high-profile characters, including two of the Arrowverse headliners.

Welling's version isn't the only Superman slated to appear. Tyler Hoechlin, who has been the Arrowverse' main version of the character, is supposed to show up.

Brandon Routh, who played the Superman in the 2006 movie "Superman Returns," has been part of the Arrowverse for years. While he's normally The Atom, he's also playing another version of Superman in the cross-over. A Superman that hasn't been announced to appear, at least as of yet, is Dean Cain. Cain starred in the series "Lois and Clark: The New Adventures of Superman." He has also guest-starred many times on "Supergirl."

Welling isn't the first "Smallville" alum to appear in the Arrowverse.

Others include Erica Durance, Laura Vandervoort and Sam Witwer.

The Arrowverse is about to change

'Crisis on Infinite Earths' is marking a pivotal time for the Arrowverse. Its lead series, "Arrow", is soon to finish its run. "The Flash", arguably the franchises flagship series, has been going through tough times. Many of its viewers have unhappily left the show behind.

It also marks the beginning of the spin-off series "Batwoman" after the character was previously introduced. "Black Lightning" has been on the air for some time, but was specifically kept apart from the Arrowverse. Now, it's to be included.