DC Universe's Titans was supposed to have the Doom Patrol return in the original version of the season 1 finale. The Teen Titans live-action drama had several ideas changed at the last minute towards the end of their first season. Originally, Titans Season 1 was going to end with its 12th episode before the showrunner had a change of heart, which led to the Season 2 premiere "Trigon" being both a conclusion to the first season while setting up the majority of Season 2. One of the major changes which got cut from the original Titans Season 1 finale was Dick (Brenton Thwaites) becoming Nightwing.
Instead, viewers had to wait for another thirteen episodes to see the former Boy Wonder suit-up as Nightwing on Titans. One of the biggest moments from Season 1 was the introduction of the Doom Patrol, especially considering how it related to Beast Boy's (Ryan Potter) background. The 4th episode, which was named after the group, was also unofficially a backdoor pilot to set up the Doom Patrol spin-off which was planned for after Titans Season 1. While the characters were eyed to reappear later on in the first season, fans never saw the Doom Patrol again after Gar left with the Titans. However, it turns out another cut from the original finale actually had the patrol back with the heroes.
According to a new series of photos Titans director Boris Mojsovski recently posted to Instagram, the Doom Patrol was in fact back for the season finale. The pictures reveal the return of Rita Farr a.k.a. Elasti-Girl (April Bowlby) along with stand-ins for Robotman and Negative Man. It is unclear whether or not Bruno Bichir's Niles Caulder would have been in the finale or if Timothy Dalton would have appeared instead. Mojsovski describes in his post that this is something which happens a lot in the TV/film industry, where something which has already been filmed may actually never be used in the final cut of a product.
Based on the photos, it would have still been the Titans' version of Doom Patrol which appears rather than the version the spin-off series follows. Despite being an off-shoot from Titans, it has been established the Doom Patrol show exists within its own continuity, at least for the time being. As far as future crossovers go between the two shows, only time will tell if that possibility ever becomes a reality. Not only do they shoot at different times in the year, but Titans films in Toronto, Canada, while Doom Patrol shoots in Atlanta, Georgia.
Had the Doom Patrol still been in the original cut of the Titans Season 1 finale, it would have possibly made the connectivity between the two shows easier to explain. The synopsis for Doom Patrol stated it would be set "after the events of Titans" which could hint at the two shows having been set in the same universe originally. With Season 2 of Doom Patrol currently filming and Titans Season 3 set to start production sometime next year, fans can only cross their fingers for a potential reunion between the two groups in the future.
Source: Instagram