In which gundam series prince betrays his sister and joins federation?

I believe it is one of the Mobile Suit Gundam series because protogonists uses that huge Robo suits to fight against Earth's federation who want to capture the princess and steel their alien tech.Federation seems having military having advanced spaceships and weapon technology.Princess lives in her giant mother ship.
There is a room on ship perhaps the room where most powerful suit is placed hidden from ship's crew only princess has the key but room is so protected that no one can enter there not safe atleast.
In episode princess drops a dagger to protogonist to call the mysteries gundam very powerful having ability to join machecally eith other Suit eventually becoming very powerful

I think I answered your question on Yahoo Answers but it might be Gundam 00. I haven't watched it personally..i Google-searched for possible answers. lol

Thanks but that didn't help me,I already checked 4-5 gundam series it's none of them!

Up up up up, Chúc ch? th?t d?t hÃ*ng

In which gundam series prince betrays his sister and joins federation?

I believe it is one of the Mobile Suit Gundam series because protogonists uses that huge Robo suits to fight against Earth's federation who want to capture the princess and steel their alien tech.Federation seems having military having advanced spaceships and weapon technology.Princess lives in her giant mother ship.
There is a room on ship perhaps the room where most powerful suit is placed hidden from ship's crew only princess has the key but room is so protected that no one can enter there not safe atleast.
In episode princess drops a dagger to protogonist to call the mysteries gundam very powerful having ability to join machecally eith other Suit eventually becoming very powerful

Honestly, I don't remember a gundam series that contains all of what you said, and I've seen nearly all of them (although, I stopped at Gundam 00, as the series went too far away from its roots for its own good).

Is this by chance Mobile Suit Gundam AGE?

The don't have a prince in Gundam00

Unless it Gundam seed or Gundam unicorn?