Spoily question about plot point in Captain America Civil War

I just saw the reveal that Bucky Barnes killed Iron Man’s parents, and Iron Man angrily asks Cap “Did you know?”

Rogers says he didn’t know it was Buck.

Stark then repeats “Did you know?”

And Rogers replies “Yes,” and now they’re all fighty again.

I don’t get it. Did he know what? If not “that Buck killed his parents,” then what?

That they were killed, not dead by an accident.

He knew that Hydra killed Stark’s parents, and he knew that Bucky was Hydra’s top assassin. He couldn’t be sure that it was Bucky himself who did it, but if he’s being honest (and he’s Captain America; he’s being honest) he knows that it probably was.

Ah got it okay.

Don’t a hundred percent know why that made Stark so mad. But I now understand the basic issue at least. (I had to divide my attention during this whole scene so I may have missed some things.)

Also, minor detail missed here, when Cap first says he didn’t know it was Bucky, Stark responds with “Don’t bullshit me.” He’s calling out Cap for lying.

but come to think of it…when and how did Steve learn about Bucky killing Tony’s parents? Was that ever explained?

ComputerZola implied it during the Winter Soldier

He’s mad because he’s still a spoiled rich kid. Cap didn’t kill his parents, didn’t know anything specific to tell Stark, and there’s probably a lot more things Stark knows that he’s not telling Cap. He’s just being a brat as usual.

uhhh - did you miss the end of the movie?

Cap - I didnt tell you because I was protecting myself from the reality of it.

“he’s my friend” “I thought I was your friend”.

Its a betrayel (in Stark’s eyes, especially with all the other info on top of it) - has nothing to do with Stark being a brat.