rose question

Trace the new growth back to the bottom and see if it is growing from below the graft (the knobbly bit  ) if it is then with a quick downwards jerk you should break it off with any attached buds, so that it doesn't grow again. If you just cut it off they tend to regrow

If it is from above the graft, then you just have a nice new branch growing

I've had that happen Monsta, and yes, it is the wild rootstock used to give that rose more hardiness.  Those suckers must come off and be kept off as they'll eventually overpower the grafted rose which will die off.