Basically you were planned to have the Beast titan so Zeke was assigned as your trainer and mentor...it was a day before you had to inherit the beast titan...he was proud of you...you were smoking outside by the drying laundry...you were talking with him but then he looked to you

"When you inherit the titan your going to have all my memories and learn my secret..."

When you asked him what his secret was he bluntly said before stomping on his ciggerate

"The way I wipe my ass...its real special"