The writer of the Outlander books will speak at the Old School Beauly to open their book department on May 14.
Demand for tickets was so high that the talk has been moved from the shop to nearby Phipps Hall, which can accommodate 200 people.
Since announcing the event, owners William Crawford and his wife Helen have also fielded inquiries about the author’s appearance from around the world.
Mr Crawford said they had contacted Ms Gabaldon on the off-chance that she might do a talk and book signing to mark the opening of the shop’s new book department, with proceeds from the event to go to Highland Hospice.
He said they were “delighted” to have received a response from the author.
Mr Crawford said: “I think we had a slight advantage as our business is right next to Beauly Priory, which is mentioned in her stories.
“We really are at the heart of the key Outlander locations here.
“Perhaps when an email arrived in her inbox from Old Schoolhouse Beauly, it gave us a bit of an advantage.
“We thought about getting a local author in to help launch our new book department but most of them have already done events with us.
“We thought about Diana Gabaldon and my wife just sent her an email. It was very much a case of ‘well if you don’t ask....
“She got back to us and I have to say she sounds like a genuinely lovely person and she has been so encouraging to us.”
It is understood that Ms Gabaldon is due to be attending other events in Scotland around the same time.
Her Outlander books have been adapted into the hugely successful television series, which is based around
around Clan Fraser in the run up to the Battle of Culloden.
The seat of Clan Fraser of Lovat, Beaufort Castle, is around our miles from Beauly.
Beauly Priory is where the character Claire Randall, played by Caitriona Balfe, meets the seer Maisri in the show, which also stars Scots actor Sam Heughan.
Originally, only 30 or 40 people had been scheduled to attend Ms Gabaldon’s talk in the shop.
But it soon became clear a bigger venue would be required, Mr Crawford said.
He added: “When it was first announced on line, we had an inquiry from someone who wanted 30 tickets straight away so we knew demand was going to be high.
“Also, we are raising money for Highland Hospice, so obviously we wanted to support them as much as possible.
“When I got to work on the morning they went on sale, there was someone here just after 7am and then they just kept coming in. People were very keen.
“People have driven from all over Scotland to come and get the tickets and then we have had inquiries from Australia, the States and Canada....people who are going to be in Scotland at the time.
“This is really a different level to what we have done before at the shop and it is obviously great exposure for us.”