Usually, in nature the two species will not mate. However, we have seen owners of Mute Swans and Australian Black Swans intentionally breed the swans. It is not good. The swan is a hybrid (cross) between the two species and is called a Blute, but is not something that is desirable.

The two swans however, should become pals if they have no other mates. Having said this, they may try to mate without success (just because of the increased hormone levels during mating season) or they may not accept each other and begin to fight during mating season. This is going to be a wait and see prospect to determine if they will accept each other as pals and not have any major sustained fights. The Regal Swan