It's obviously Tim Drake. Red Robin was merely a ruse to catch Dick and Damian off-guard, since neither would expect it. This way, he can get back into their good graces, spy on them, and maybe even get Damian to develop a crush on him before ripping off the mask and BAM! A trap is sprung.
And you all thought Bruce making him cross-dress as "disguise training" was just some one-off. HA!