Educate Me Please

I had a great weekend working in the yard and planting flowers to add some color to my patio and front porch. I even bought my vegetable plants for the garden. I can't wait to get them in the ground and growing.
As I was pondering what to do with some of my rose bushes I looked at one in amazement. See, I planted 3 different roses about 4 years ago and the one that has done the best is my Silver Bell rose. It looks like a light lavender color and is the stem rose that you see in arrangements. Well, to my surprise there is also a red rose growing with my Silver Bell that I did not plant. ????? When I say it is growing with my Silver Bell, I mean that it is literally growing from the same root system. See the pictures!It really had me scratching my head. I am not an avid rose grower and I do not know much about gardening so this really had my mind going nuts.
So, I thought I would ask my Bloggy friends what caused this. Can someone out there educate me on this please?
The roses are really pretty so I am not complaining that they are there. I will just enjoy them. I just want to know what happened. :)