Likely, the male will not accept this female. This may be that she is too young as 1.5 years of age is usually not old enough to successfully mate. In fact, he could hurt her especially if she is not sexually mature.

Most male swans will go about their lives without re-mating. Since this male has already had two mates, it is not likely that he will take a 3rd. This may not be the case with the introduction of another female, but it is something that we would recommend be done extremely cautiously. If the male is trying to pluck this female's feathers, it is indicative that he does not want another mate or swan in his territory. It would be better to remove the female and find her another mate and home.

As far as the cygnets, he may even try to hurt or kill them as they turn white and he tries to remove/chase them from the pond. You will need to be alert for their safety and ensure that he does not try to mate with a younger female cygnet.
The Regal Swan