Alpha Ebert had noticed somebody defending the Litha Moon pack with a speed that scared him. At this juncture, he could taste his failure, which would bring him nothing but shame. Also, he was close to losing his pack and title if he so lost this war.
With his army falling so quickly, the shortcut was to eliminate Alpha Idris. If the Alpha dies, the war would forcefully be brought to an abrupt end.
Just as he got Alpha Idris where he wanted and was about to exact his final blow to kill him, Alpha Denzel appeared from nowhere.
Having shifted from their beasts into human form, they faced each other squarely, the medical team used the opportunity to attend to Alpha Idris.
There was no information that Alpha Denzel was an ally of the Litha Moon Pack. If Alpha Ebert knew this, he wouldn't have attacked.