Whos the Rat? er...Lion?

A lion was getting married. At his wedding was a mouse shouting away
and congratulating the lion
"All the best, my brother. Good luck."
Seeing the mouse shouting away claiming that the lion getting married
is his brother, another Lion grabs the mouse in anger and asks: "Who
the hell do you think you are? How can a lion be your brother? You are
only a mouse."
The Mouse replies:
"I, too, was a Lion before I got married."