They knew, when they were summoned to the ministry, that it was a matter of life and death, that the fate of the worlds, wizard and muggle alike, hung in the balance. They knew as they stormed the Department of Mysteries. But as Sirius stood wand-to-wand with Bellatrix, laughing as he dodged her spells, he was back at Hogwarts.
Prongs stood, grinning, at his side as they faced down the victims of their latest prank while Wormtail, cheering madly, and Moony, trying, but failing, to concentrate on his book, stood amidst the numerous spectators.
"Come on, you can do better than that!" Sirius taunted, ducking away from the red flash of light. The second curse hit him squarely in the chest, launching him back into reality. As he fell, he caught sight of Harry and Remus. Shock mingled with fear, not for his own fast-ending life; not even for Harry, James's son, his godson; but rather for Remus. Moony. His Moony. Whom he'd lost for twelve years while in Azkaban.
Silver eyes met gold and they knew that this was the end. It was so like last time, Sirius was being torn away, without so much as a goodbye, but this time there would be no miraculous escapes, no heart-wrenching reunions. This time there was no turning back.
He was gone. The world seemed to go silent as the whispering veil engulfed him. Remus seized Harry, who fought to go after Sirius.
"There's nothing you can do, Harry . . . nothing. . . . He's gone." The boy struggled still harder, shouting desperately for his godfather.
"He can't come back, Harry," his voice broke as he forced the words from his mouth even as each broke his heart a little more, but Harry must not follow Sirius. "He can't come back, because he's d-" his thought was cut short by Harry's continued cries. The truth of his declaration overwhelmed him. Like drowning in lukewarm water, it was suffocating. The pain lacked both the numbing depression of the cold and the vengeful fury of true heat but the hopeless emptiness was there, amplified by the wolf's feral despair at the loss of it's mate.
They'd always known this day would come. But that didn't ease his suffering. Knowledge was power, even more so than magic, Remus believed this with all his being but time can never heal all wounds. Sometimes nothing can be gained by simply knowing.