How do I find the vector behind and 45 deg bellow player

I am new to the engine and have so far been able to figure out everything from the forums and stuff. But I couldn’t find an answer to this one anywhere. What I want to do is run a line trace from my players current position (not cam) to a point exacty behind the player and down at an angle of 45 deg from player, so it should intersect with the floor behind the player. I rotated the vector by 45 deg on the x axis and it works great as long as your on spawn facing exactly straight on the x axis. But if you turn the character it messes up the angle.

How do I rotate relative to the player but get world coords for the line trace.
Thank you,

Nevermind, I figured it out. Here was the trick.

Basically, get the yaw rotation of the player and then add the desired pitch, get the forward vector of that multiply by -1.