Thread:MDGeistMD02/@comment-25480373-20170821020503/@comment-25480373-20170821021948

Here's the whole thing from the section copied and pasted for you to look at:

Between Arkham Origins and A Matter of Family IncidentEdit
Some time between the New Year's Eve Incident and the Joker's takeover of Arkham Asylum, Gordon was promoted to Commissioner. During that time, Gordon had deduced from Bruce Wayne's witness statement several years ago that the billionaire himself was Batman, but decided that it was best that the world never know. This allowed him to trust Batman better, since this assured him that all Batman wanted was to ensure that the criminal element of Gotham wouldn't be able to harm other families like Waynes had been.

In the years following his promotion, Gordon eventually formed an alliance with Batman. However, unbeknownst to Gordon, his daughter, Barabara, had also joined the Dark Knight as Batgirl (a direct result of Gordon preventing her from joining the GCPD).