This is not confirmed and may be fake but it is the leak circulating on the internet
According to the leaks, Azrael and the dark angels release a battle against the forces of Vashtorr, they were boarding fights, the ships were invaded and they fought between small groups, then Abaddon and his forces arrive but at that moment Dante arrives with a large fleet and full of Blood Angels and they stop Abaddon.
Until Angron arrives with all the fleets he corrupted, the balance is on the side of chaos.
It turns out that what the key does is destroy the Eldar webway, so it would destroy Terra since in the Emperor's palace it is connected to one of those portals but in turn that made an Eldar fleet go to help because that would also wipe out all the eldars, after the Lion arrives and teleports to Angron's ship, they fight but the Lion wins.
Azrael defeats Vashtorr, seeing all that Abaddon flees.
In the end Azrael orders all the surviving Eldar to be executed and takes the leader to torture him, Dante scolds him because they saved them but Azrael clarifies that it is very risky for the Xenos to know that in The Rock they guard a weapon that can destroy the Imperium ( the dark angels guard the key in The Rock).
In the end, the Lion did not stay with his children but went directly to see Guilliman, to talk to him.