Well i agree that this was such a bad development. While i already anticipated this silver being Deliora was so forced. But what i truly feel awkward was not the truth of Silver is Gray's father, but how it is revealed. It's too generic and bad for my taste the situation "i actually your ..... and don't plan to kill you all along", this will resort on another flashback to justifies Silver reason. He just can say he is Gray's father from the beginning and it's fine with me.
And if Gray know about it, why he not say it and try to discover Silver motive instead beat him and complained afterwards? bad forced twist.
And Ultear isn't dead, isn't? she just retired because she is too old.