Glorfindel had known the moment Oropher and his Silvan troops charged that things would go poorly for them. Gil-galad had yet to give the command, but Oropher was too proud, too unwilling to submit to the High King's rule to await his signal. He had known in that moment that it would be his downfall, but there was nothing he could do to stop it. The only way they had any hope of beating Sauron's forces was to follow the plan that had been laid out, despite Oropher's brash actions. The Last Alliance needed to remain as cohesive as possible, a well-oiled machine, with as many separate pieces as it had. There was no more room for error.
When they were loosed, Glorfindel did his best to drive his own small contingent toward their wayward allies, but he could see the damage had already been done. There were too many foes- orcs, trolls, even men- to reach them in time. If Oropher had not been so stubborn, three years ago he could have sent troops to Imladris, where they would have been able to share in the forging of greater armor and weapons, but he'd stayed in his borders until the last possible moment. His troops were ill-equipped, unable to withstand the host that surrounded them. Hours passed before his Noldor were able to get anywhere near them.
Amdir's troops to the west were lost to them, Glorfindel could see the press of the Enemy wedge between them, cutting them off inexorably from aide. He did not, however, see Oropher's fall. His shield, an updated replica of the one he had lost in Gondolin, presumably buried with his corpse beneath the waves of Belegaer, was already slick with black blood on its sharp edges, dulling its golden shine. A classic symbol of defense, it had always been the key player in his offense, deceptive and deadly, working in tandem with the longsword in his right hand, both extensions of his own limbs. For now they were still light in his hands, but with the troll bearing down on him that did not make it easy. When it fell, finally, from a final shot from an unseen archer at his rear, that was when his path cleared enough to spot familiar silver hair.
It was the odd movement that caught his attention at first, as he climbed over the fallen corpse, an unwise decision to put himself any height above the battle, given that he already shone like a beacon with Valar-given power, but his fear of death had died long ago. Glorfindel's eyes followed the off-kilter movement, responding oddly to the stimuli around him. It was as if he was moving at an angle to the rest of them, disengaged from reason. He moved forward, pausing only long enough to cleave the head from an oncoming orc, as he called Oropher's name. But no, that was not Oropher, he realized a moment later, and then he understood what was wrong.
Glorfindel broke into a run, using his shield as a battering ram to force his way through the mob. He heard the crack of a skull as a man with kohl lining his eyes and tattoos covering his face bounced solidly off the engraved flower on his shield. He called Thranduil's name, but he doubted he could hear over the sounds of battle around them - if he wanted to hear at all.
He hadn't seen his father in many years. The decision to stay behind in Lindon, while his father crossed Ered Luin and then the Misty Mountains to rule the Silvan Elves in Greenwood the Great, had been a hard one to make. But Thranduil had made it. He had only just recently gotten married when Oropher decided to leave, and Thranduil had seen no reason why he and his wife needed to uproot their lives. Eventually the two of them would make the journey because Thranduil was his father's only heir. He didn't expect anything to ever happen to Oropher which would cause him to take his father's place but, just because he didn't expect anything to happen, it didn't mean that nothing would happen.
And then came the call to march upon Mordor. There were not many Elves in Lindon who wished to resist the call. Regardless of what his father had planned to do, Thranduil would have gone with Gil-galad. What hope did the alliance of Elves and Men have against the hosts of Mordor? Not much but something needed to be done. When they had gotten near to the Greenwood on their march, with Gil-galad's permission, Thranduil had taken a small host to ride ahead and meet up with his father's own party. Thranduil wished to fight alongside no one other than Oropher in the battle to come.
That battle was brutal from the beginning. Thranduil had foregone a shield, dual-wielding swords instead. He had tried to talk his father out of charging so early but his words were not heeded, and Thranduil had joined the fray with the Silvan Elves. Orc and Man went down beneath his blades quickly, and he saw that his father was doing just as well. But, despite his best attempts to remain at Oropher's side, they eventually became separated. Thranduil didn't think twice about that, until he caught a glimpse of a large group of orcs clustered together around a single foe of theirs.
When Thranduil saw his father standing there all alone, he did all that he could to reach him in time but his best attempts were to no avail. His father didn't see his own death blow as it came from one of the orcs standing behind him. "FATHER!" Thranduil shouted out, his voice barely above a whisper in the cacophony surrounding him. Paying no heed to his own safety and, even if he didn't know it, not walking in a very straight line, Thranduil stumbled over to where his father lay.
Oropher was already dead. Thranduil had even been robbed of the chance to say goodbye. He knelt down beside him and cradled his head in his arms, planting a tender kiss on his brow. The battle was still raging on all around him but Thranduil was in his own private world of grief. He didn't see the two orcs approaching from behind him. Even if he had known that they were there, Thranduil might not have done anything to stop them.