The Prince of Wales joked he was "very grateful indeed for the perfectly kind wishes about my rather slowly-approaching grandfatherhood".
Charles said during a visit to West Yorkshire, "Some of you may have realised that with grandfatherhood comes, in four months' time, old age pensionerhood".
The Prince added that he hoped he had "a long shelf-life".
Warning: This video contains flash photography:
More top news
Minister will fail to eliminate the gender pay gap in a generation if it continues to "ignore" evidence to help achieve its goal, MPs warn.
Report criticises ministers for lack of long term plan to recruit and retain teachers in important subjects such as physics and maths.
Emergency services rushed to the scene to douse the flames, but there were no immediate reports of casualties.