The stars were on a break from filming upcoming BBC TV comedy Blandings in Northern Ireland last week (ends06May12) and they happened to be present for Alan and Nicola Forbes' celebrations following a ceremony at Crom Castle.
Nicola tells Britain's The Sun, "It made our day, we're so lucky. The wedding was already unbelievable and everything was outstanding, but what really made it was David turning up. We'll never forget it.
"No one could believe it. Then he had everyone in stitches when he jumped for my bouquet."