Today, The CW unveiled the official synopsis for the fifth episode of Arrow's fourth season, "Haunted." This episode will see the first appearance of John Constantine on the show:
“Haunted” — (8:00-9:00 p.m. ET) (TV-14, LV) (HDTV)
MATT RYAN REPRISES HIS ROLE AS JOHN CONSTANTINE ON ARROW — When things take a turn for the worse with Sara (guest star Caity Lotz), Oliver (Stephen Amell) calls in a favor from an old friend who deals in the mystical, John Constantine (guest star Matt Ryan). John Badham directed the episode written by Brian Ford Sullivan & Oscar Balderrama (#404). Original air date 11/4/2015.
So, as you can see Constantine will be brought on the show after Sara's resurrection and will have to deal with the side effects of the Lazarus Pit on her mind.
Will we see Constantine in the flashbacks ?
What's more interesting about this synopsis, is that his character will be introduced as an old friend of Oliver. We already know that during his five years away, Oliver had to deal with magical things that we haven't seen yet. Thus, Ollie probably met Constantine during the 2 years that we still have to discover.
We were wondering if we would get to see John again on Arrow, and more broadly on the DC TV Universe. I'm pretty sure we got our answer with this synopsis. The flashbacks always showed us everything that happened to Oliver during his "five years in hell." So, expect to see John Constantine again this year or maybe next season.
Even if the flashbacks are good, I'd like to see Constantine involved in the main story but anyway I look forward for his next appearance.