He is the Duke of Ramblingham and the father of Lady Joy. He along with his daughter paid King Roland a visit to discuss plans on building a new bridge after an accident involving a parade of 104 elephants. Apparently, he moved 103 elephants across the bridge, then tried to move one more, and the bridge split. While his daughter unknowing spent time with the Bad Sofia, he worked on a model of the new bridge with Roland and the Royal Builder. Apparently both Lord Gilbert and Roland got carried away with the design and kept making so many changes to the model which ended up being knocked down by Bad Sofia. After the Royal Builder rebuilt the original design, though with gargoyles on the midsection, Lord Gilbert and Roland liked it.
He made a short non speaking appearance at Roland's birthday party in "Her Royal Spyness".
Roland was exhausted by his presence, just as he was by King Magnus in "Cedric's Apprentice." Roland mentions a "You-Know-Who" and a "You-Don't-Want-To-Know-Who" in The Curse of Princess Ivy who aren't supposed to sit together. Looking at how Gilbert and Magnus are both exasperatingly competitive, it's likely Roland was saying Gilbert doesn't get along with Magnus.