At the mention of limbo, Cas felt a strange feeling pass down his spine. That sounded...oddly like Purgatory, though in his reality, he'd only heard rumors. There were reasons why it was hidden where he was from, or so he felt. It was the kind of thing that could only be opened when Heaven had no other choice. Yet, since it was likely different for Piotr, he was willing to let it pass.
Sighing, he looked up. "You do have a point," he agreed. "Yet for what it's worth, I'm sorry you had to kill anyone at that age. Unless it was something you chose for yourself, in which case, it is simply that."
How to put it was always a mystery to him. As an angel, it had never been a consideration and merely a statement of fact. Keeping the truth hidden had never occurred to him until Dean had prompted him to do so during their search for Raphael, though...seeing as his siblings had never cared much for obfuscated truths, Cas supposed it was just one more thing that set him apart from the others.
"I...served in Heaven," he began bluntly. "For centuries. God created me to serve and carry out His will. That is at least, until we found that God was no longer giving the orders and the archangels had an agenda of their own. It is to my knowledge that my mate and I were not the only ones to rebel, though many were killed in the process."
Granted, he should have rebelled much sooner than he had. Or perhaps not. To Cas, it had always been a source of further confusion. He regretted not being completely honest with Sam and Dean and regretted betraying Anna even more, but...it had definitely been a simpler time.