This is how Cassandra learns of Thanos' death goes in Echoes.
[Elsewhere, Cassandra and Yoda search the street as she finds a tape]
[She puts it on the tape recorder and sees a recording of Mac cutting off Thanos' head]
Cassandra: [gasps]
Kovu: [on recording] What did you do?
Mac Grimborn: [on recording] I went for the head.
[Mac walks away as Cassandra turns off the recording]
Cassandra: Why?
[As she heads outside, she couldn't believe what she witnessed]
Cassandra: I can't believe it. I need to find him. If anyone knows where Mac is, it'll be Baylan.
[On Mustafar, Cassandra talks to Baylan]
Cassandra: When was the last time you saw him?
Baylan Skoll: Just yesterday, he said he had important business on Dathomir. Why do you ask?
Cassandra: I have to find him. Baylan, Mac killed Thanos.
Baylan Skoll: How do you know about that?
Cassandra: I saw a recording. But before that, I've been hearing whispers of him killing the rest of his followers.
[Baylan knows why she wants to see Mac. On Dathomir, R5 detects Baylan's shuttle and alerts Mac]
[Mac runs outside as Cassandra hugs him]
Mac Grimborn: What are you doing here?
Cassandra: I was so worried about you. I know you killed Thanos.
Mac Grimborn: Who told you that?
Cassandra: I saw the recording. I also heard the rumors that you wiped out his armies and hijacked his ships.
Mac Grimborn: Thanos was the reason I'm an orphan. I had to do it.
[Zira watches from afar]
Mac Grimborn: When I came here, I felt the power of the Nightsisters. I realized that I am more powerful than the Overlord. I can return him to dormancy.
Cassandra: How?
Mac Grimborn: I need to lure him away from his support systems, so that I can catch him.
[Zira growls]
[Cassandra feels worried]
Cassandra: Mac, I can't believe I'm actually saying this, but I understand why you killed Thanos. The truth is, I fell in love with you.
Mac Grimborn: What? But why? My face is burnt.
Cassandra: It doesn't matter. I also know why you left the Jedi Order.
[She takes off Mac's helmet and kisses him]
[Zira runs away as we see the Overlord having heard everything Zira had told him]
The Overlord: What?! You are certain of this?
Zira: Yes, my lord. I saw it with my own eyes.
The Overlord: [growls]
Allura: We swore to ourselves that we would win this war, but now our army is shattered. Literally.
General Grievous: Yeah. When you think about it, all Scar gives us to fight Grimborn and his squad is Crystal Warriors.
[The Overlord glares at them]
General Grievous: Um, metaphorically speaking.
Hexxus: Guys, what's with the doom and gloom? I'm actually okay with it. I've been looking up on some new jobs and they're awesome. Check it out. This one has shipyards on Corellia.
Opaline Arcana: Ugh, Hexxus.
The Mechanic: Jobs? No way! I'm a terrorist! I have a driver's license.
Hexxus: You don't need it, because these Star pilots don't let you drive. But get this, the Ministry of Magic's hiring new Azkaban guards since the Dementors vanished into thin air.
[Grievous growls]
The Overlord: Hexxus! Ugh, never mind.
[They watch everything on Dathomir]
Flotsam: Ugh, gross.
Jetsam: Same.
Cassandra: Mac, I want you to know that you're a good man.
[Mac smiles and holds her hand]
Doctor Doom: Ugh.