Clonegrim wakes up from thousands of years of stasis into a scene of chaos. Nearby Iron Hands legionaries may also have come out of stasis and see him with their dead primarch at his feet.
"It wasn't me!" testifies Clonegrim sword in hand.
"Objection!" roared various Iron Hands who may or may not have bore witness to Fulgrim committing the very act on Istvaan V. They express their grief and hatred with a rain of bolter fire.
Flavius Alkinex, and other members of the Emperor's Children, who were traded away by Fabius, are also present at the scene and return fire to protect their returned primarch.
Clonegrim steps into the line of fire to prevent any more bloodshed on his behalf and kick-off his redemption arc. He makes a passionate speech that is both logically sound and emotionally cathartic prompting a pause in the gun fight.
"I have no reason to forgive you, but we're now surrounded by these metal skeletons who are somehow a higher priority target than the person I saw kill my genesire." said the Iron Hand.
Flavius heads over to a freed Saul Tarvitz to have a broment. "We should never have left you brother. You were the best of us."
"I just got here and this is a lot to take in, but me and my boys are leaving. I should just leave all of you here but forestwalk lets me Deus Ex Machina my way into anywhere. I'm sure Black Library will have me visit Solemnace officially at some point for bullshit such as this." exposited Lion who'd just forestwalked his way into the scene.
"Go! Me and my irredeemably chaos tainted warriors will hold off the spoopy robots, and exit the narrative heroically!" shouted Flavius Alkinex
"Based." concurred Lion, who had not killed these warp-tainted traitors on sight.
"But I don't want to leave any more of my sons!" objected Fulgrim even as he retreated towards the poorly defined extraction point.
"Only from the ashes shall the phoenix rise again!" argued Flavius Alkinex, who had almost always been portrayed as an asshole in each of his official appearances.
"Are we still alive?" asked the Iron Hand on behalf of his legion and some Great Crusade Era Salamanders who may also have been freed from stasis in the chaos.
"I don't know. It would be out of character for me to leave any servants of the imperium here if I could save them, but none of you are relevant to this plot." answered Lion.
"I'd prefer if you left them." opined Trazyn from off-screen. He was likely distracted by the mysterious harlequin as portions of his museum were being repatriated or vandalized.
"For the Phoenician!" shouted Alkinex as he and his fellow Emperor's Children died heroically to speed-run their redemption arc despite thousands of years of sexual war crimes.
Clonegrim and Saul Tarvitz looked back at their doomed brethren as they retreated into Mirror Caliban with the Lion. They vow to recall the memory of their heroic deaths whenever it became dramatically appropriate.
"Learning to forgive you may be part of my character arc, but let's not talk about it right now." says Saul to the clone of his gene-father.
"I shouldn't quite trust you and your company of loyalist traitors, but I'm going to have to turn you and your company into primaris marines in order for you to survive the sheer amounts of femstartesussy you're about to drown in." said Lion to Saul in an appropriately sombre setting.
"I guess I'm going to have to adopt the codex astartes to organize my company of Emperor's Children, Luna Wolves, and World Eaters." replied Saul.
"But wait there's more!" offered Lion. "Since you don't have any Death Guard, I'm also reinforcing your company with fresh primaris recruits that happen to have the complete set of Istvaan 3 gene-lines. And this is on top of the new tech we're issuing you for this suicide mission."
Clonegrim ran his hand through his new haircut. "Brother, why did you force me to get this haircut that makes me look like a lesbian?"
"Because we're bringing a company of Sons of the Phoenix who instinctively recognize you as their primarch. And if they find out you're not Rogal Dorn, then it'll break their hearts." answered Lion.
"Of all the chapters you could have chosen from, why are you bringing religious zealots? Weren't you recently outed as anti-ecclesiarchy?" asked Fulgrim looking kind of like Nero as he appeared in Devil May Cry V.
"Because conveniently there aren't any other chapters available. And I would feel less guilty sending them off on a suicide mission." Lion explained.
"Aren't you and your Risen also coming with us on this suicide mission?" If Fulgrim showed any sign of worry from being sent on the same suicide mission, a mere mortal wouldn't have been able to detect them.
"Because I can always forestwalk away." boasted Lion. "Now onward into this poorly explained phenomena that the premise of this story is built upon!"