Quite apart from their uncanny brilliance, the Holmes brothers were as different as night and day.
Sherlock was born to be a drama queen, loud and blunt about as much as his brother was secretive and reserved. Pale and untouchable, that was how Mycroft appeared to the rest of the world; a man cloaked in sorrow, silent and subtle and deadly if compared to mere mortals.
Greg liked them both, no matter that Sherlock drove him up the wall on many an occasion – whilst Mycroft kept him at arm's length all the time. He was quite surprised when the younger Holmes showed up at his favourite pub one evening, as if trying out fellowship the way ordinary people did; time for Peter Pan to grow up, he thought as he watched Sherlock's clumsy attempts at courtship – which Molly Hooper didn't seem to mind at all.
For all that the consulting detective couldn't help but scoff whenever sentiment was mentioned, it looked like even he had yielded to the lure of companionship at last. And somehow, Greg found himself wondering how likely it was for the elder Holmes to meet his Waterloo as well, someday.
xxx
When the moment came, it was less of a Waterloo and more of a Treaty of Versailles. Mycroft Holmes making peace with his own feelings was a sight to behold, and Greg couldn't quite believe he was the reason for that to happen.
Never in a thousand years he would have dreamt of being entrusted with Mycroft's heart – a thing of beauty if there ever was one. Now he knew how the Little Prince must have felt when he finally tamed the Fox, as was told in the book he'd read in his childhood.
It was the sight of his partner walking hand in hand with his niece along the shore that first planted the idea of adoption in Greg's mind; if Sherlock could make for a good father – all things considered – then the role would definitely suit Mycroft even better.
The little girl that eventually became a part of their family was the closest to a Holmes he could ever imagine; she was smart and quirky, and shared her uncle's talent for the violin.
It warmed Greg's heart to see Mycroft shed his cloak of sorrow just for her.