Technicaly, in the second movie, it explains that there where seven primes in the beginning that where the leaders of the Transformers. When they went looking for Energon by blowing up suns from distant planets they followed only one rule. not to destroy a planet with life.And then they went to earth.One of the Primes hated humans and wanted to destroy them by putting on the machine they used to blow up suns. They named him The Fallen. (So yeah, The Fallen was a Prime.)
As for Megatron, Optimus and the fallen being brothers... Technicaly, Optimus and the Fallen are related since they're both Primes. for Megatron to get in the mix, they all use Energon to live so they must be related. But in a way I think Optimus uses the term brother openly as "we are both the same regardless".
Optimus and megatron are brothers,the only reason that megatron is not a prime is because back on cibertron,when optimus and megatron ruled,Optimus was fair,thus making him a prime,and megatron was firm,so he was called lord high protector.so yeah,they are brothers.
After watching Transformers II and paying close attenetion when Sam dies, there are 6 primes standing there talking to Sam. Megatron is not a "Prime". "The Fallen" is one of the original primes which makes 7, and Optimus is a decendant of them.
megatron anD Optimus are brothers ("you left me no choice, brother". and various over canon sources
Optimus is a descendent of the fallen, (as stated by the other 6? primes "you have fought for optimus our last descendent")
and the fallen is brothers with the other 6 original primes "th fallen was stronger than his brthers"
so optimus can't be his anscestors brother (like you can't be your mum's sister/brother)
but at the end of RotF
the fallen "die like your brothers"
optimus "they were your brothers too"
so i'm not sure but i think that when The Fallen said that to Prime he just meant because they(other 6 primes) were Primes and so is Optimus.
just be glad its not as bad as the G1 constructicons origin, huh?
since all the highest in command at cybertron are primes and only a prime can kill a prime, that should indicate that megatron is a prime.
so they all should be related (but not brothers)since the fallen is way older than optimus and megatron.
No the fallen is one of the original Primes he just betrayed his brothers
As for megatron, he and optimus used to be friends while he was a gladiator before megatron became a freedom fighter and eventually became mad with power and ......EVIL!!!!!!
The Fallen was originally Megatronus Prime. Megatron named himself after him before he became leader of the Decepticons. Optimus was originally Orion Pax, and was chosen to be the last Prime. They're not actually related. Optimus calls Megatron "brother," because they were close like brothers before the war, but not literally brothers. Realisticly, one of them may have been a decendant of the Fallen, but there are no hints to this.
Megatron isn't Optimus' brother, Optimus was once known as Orion Pax, and Megatron was once known as Megatronus (Copied name as The Fallen before having the Prime title taken off him), Megatronus was Orion's idol, Orion wanting to learn about the history and future of Cybertron, when Megatronus was going to the high council to say his vision and maybe become a Prime, he saw fit to change his name, to Megatron, he demanded he should become Prime, but the council were moved by Orion's words, this made Megatron angry, and created the decepticons, when Orion went to the heart of Primus, he got given the Matrix of leadership, naming him Optimus Prime, so no, Megatron and Optimus are not brothers.
As for The Fallen and Optimus Prime, all Primes are brothers, so if The Fallen was a prime, and Optimus is a prime, they are brothers, just very far apart.
NOTE: There brother meaning and our brother meaning are different.
optimus is a descendant of the fallen as they are both primes, in transformers lore megatron was part of a rebellion against the cybertron society for the freedom of all transformers, at the time optimus was just a desk clerk but he joined the rebellion and became good friends with megatron. which is why optimus refers to megatron as a brother