Gundam Reconguista in G

The Megafauna launches into space in order to create a distraction for the passing Amerian Space Fleet. Dellensen Samatar, Bellri's old instructor at the Capital Guards, pits an Elf Bull to leads a squad of mobile suits to once again attack the Megafauna to try to rescue Bellri. Unbeknownst to Dellensen, the G-Self was actually piloted by Bellri, and the two engaged in combat. The two eventually discovered each others' identities, but it was too late as Bellri shoots Dellensen's Elf Bull down, killing his old instructor in the process.