Welcome to rootschat tonip.
I can’t add anything useful, but I think this photo is wonderful! Even if the army chap
was a relative, it would still be odd for him to be holding his female relative’s hand in her wedding photo .... or even if this was a split second touch unintentionally captured by the photographer - still odd ... and strange that they had the photo printed rather than choose one where he wasn’t touching the bride’s hand.
I am letting my imagination run away with me here.

Did the army chap appear in any other photos, wedding or otherwise?