The mother-of-two - who first released the track in 1994 and has re-recorded it as a duet with Justin Bieber this year – said that she had no idea what a hit the Christmas song would prove to be.
'I'm amazed and humbled by its popularity, even all these years later,' she told The Sun. 'And I think it's great that people have the song as a ringtone.
'Who'd have thought, all those years ago when I wrote it, that it would still be having an impact today?'
Talking about her collaboration with the Canadian teen sensation, she added, 'Justin's definitely a young phenomenon — fun, cute and very talented. That's why I wanted to work with him.'