It'd be funny if he was like "I'm going to declare my (step)daughter as my heir"
"Oh, that sounds reasonable. I didn't know you had a new wife, let alone a daughter"
"Yeah, she's great (insert massive monologue turned soliloquy about why his wife is amazing)"
(Later)
"Can we meet your daughter so we can formally make her your heir?"
"I'd have to ask her, but I think so"
(Asks)
"She said she'd never do it"
"Why not?"
"Well, she's a teenager, and in that rebellious phase, so she doesn't recognize me as her dad much. Doesn't help that she's now out of a job after learning that I'm not a bad person"
"What was her job before, that that could-"
"Oh, she used to be the hero"