He and his wife Jacqueline are appearing on the Valentine's Day special of the ITV show to raise money for the hospice, of which he is a patron.
During filming the couple made it to the last question: "Translated from the Latin, what is the motto of the United States?" They answered "In God we trust" and were shocked to find they were wrong when the correct answer was revealed as "Out of many, one". Instead winning £1m, they had to settle for £32,000.
But afterwards Celador, the programme-maker, admitted that the question was ambiguous and did not meet its "usual high standards". As a result, it invited the couple back to resume the game with a question at the same level.
Llewelyn-Bowen said: "We feel as if we've been reprieved from the firing squad - how unusual it is to get a second chance in life, but as far as we're concerned the charity really deserves this."
Sarah Thorne, communications manager at Shooting Star, said she hoped they would only answer the question if they were sure they knew it, so they would still win £500,000 for the charity.