Your swan will be just fine on its own, especially if there are other waterfowl such as ducks, geese, egrets, herons etc.

Swans may or may not re-pair with another swan once their mate dies. If you introduce another swan, you will need to have your swan sexed by a veterinarian to ensure that you do not get a swan of the same sex. If the swan is the same sex, both swans will fight and may seriously injured or kill each other.

Once you have the swan sexed and you still want to introduce an opposite gendered swan, you may need a state permit which will require you to pinion all cygnets at 1-3 weeks, require you to be responsible for all veterinary care and documentstion. Once the cygnets turn one year of age, the parents will chase them from the pond. This means that you will need a safe health home for the cygnets.

Finally, you must build an introductory pen, enclosed top to bottom so predators cannot climb into or dig under the pen to access the new swan.
The pen should be 1/2 in water and 1/2 on bank with a zero entrance. A feeder should be placed inside. The new swan will need to stay in the pen for approximately 2 weeks. This will allow the new swan time to be acclimated to its new habitat, get used to you and your swan so that it decreases the chance that it walk away from the new habitat. If you see any sign off aggression by either swan while the new swan is in the pen, then this situation is not going to work and you will either need to return the swan to where you got it from or find it another home. You also need a boat or other rescue equipment should there be aggressive behavior once you release the new swan onto the pond so you can rescue the new swan or separate the swans from a fight.

In our opinion, you will avoid a lot of problems by leaving your swan alone. It will do just fine. The Regal Swan