"Je t'aime, mon frère."
Here's a breakdown:
* Je t'aime: This is the standard way to say "I love you" in French. It's a very formal and affectionate way to express love.
* mon frère: This literally translates to "my brother".
However, you can also say:
* Je t'aime beaucoup, mon frère: This means "I love you very much, my brother".
* Je t'adore, mon frère: This means "I adore you, my brother", which is a more intense way of saying "I love you".
The best choice will depend on the context and your relationship with your brother.