Most hellebores hold their blossoms for a very long period, although they will have likely stopped producing new flowers some time ago. If the flowers on 'Ivory Prince' have faded to green they are old flowers and you can remove them at any time. They may have developed the characteristic seed pods, which indicate the flowers are fully spent. In most cases, the presence of greenish flowers on the hybrid hellebores indicate they are spent blossoms - old flowers tend to age to a dullish green.

It is generally suggested that unless you wish to save and harvest the seeds, the flowers be removed once these seed pods begin to form so as not to divert the plant's energy into seed formation. 'IP' is sterile so no need to attempt to save these seeds. IME, once the flowers are fully developed and starting to go over is when the dreaded hellebore aphid makes its appearance, so I tend to cut back before the aphids have a chance to proliferate.

Okay, I'll remove the flowers tonight when I get home, though it kills me to do it!
Thanks for your help.