Mycroft Holmes wasn't often struck speechless. He was a very articulate man with most of the words of all of the languages at his disposal, and so was not one to be caught without the appropriate words to form in any matter presented.
Mycroft Holmes was not often surprised. He was a man of many secrets (mostly other's secrets) and was not accustomed to being caught unawares. He prided himself for being mysterious and opposing in all of his eidetic knowledge.
Mycroft Holmes was not often one for feeling immense emotions, either. He was aware, perhaps too much, of the emotions of those around him and could manipulate their feelings and imitate them when necessary to persuade and bribe those to his way of thinking.
There was, however, an anomaly and exception to every rule. Even if those rules were those of the ice man who held a 'minor position in the British Government'. Mycroft Holmes knew that this was the case but he would have never thought to have predicted an occasion when they would apply to himself.
So, being unaware of his coming predicament, Mycroft Holmes became a victim to all of these exceptions when a certain Detective Inspector dropped to one knee in their shared, too big kitchen, as it were, and asked that all important question;
"Mycroft Holmes. Will you marry me?"