They are the multi-million selling time-travelling novels which have inspired a major TV series shot in Scotland.

The Outlander TV series has filmed two series in studios in Cumbernauld and the new series opens on the Amazon Prime streaming service on April 10.

Now the author behind the Outlander phenomenon says it could well return to Scotland for a third season.

The makers of the series, Sony and US cable channel Starz, have not officially committed to a third series or that it will be shot in Scotland.

Diana Gabaldon, the American author of the era-hopping adventure romance novels set in 18th century Scotland, also a consultant to the TV series, has said thoughts are already turning to how the third book in the series could be filmed.

A third season of the show would be based on the novel Voyager, which is set in Scotland, notably the Highlands and Edinburgh, as well as on board ships and in Jamaica.

Another season could continue the economic boost to the film industry and tourism - it is estimated to have already boosted the economy by £20m.

It could also lead to an extension of the studios in which it is filmed, in Cumbernauld, North Lanarkshire.

The author, currently writing the ninth and, she says, penultimate book of the series, would not be drawn on whether there will be a third series in Scotland, but did say: "Working on the assumption there will be a third series, they will be able to shot quite a bit in Scotland.

"They are trying to expand the [Wardpark] studios in Cumbernauld to six stages, trying to make it into a major film studio, and so far all of the interiors have been shot there.

"You would need to do some other things, it is a very active story, you would need to shoot some of the show on a ship."

Ms Gabaldon suggested that Starz may be able to use the ships which another one of their series, Black Sails, use for its pirate-themed adventures.

Black Sails is shot in Cape Town Film Studios in South Africa.

She also suggested the beaches of Jamaica could be replicated by the "white sands" of the Highlands and Islands.

Ms Gabaldon, speaking from her home in Arizona, said she is thrilled by the quality of the second series of Outlander, which once again stars Sam Heughan as Highland warrior Jamie Fraser and Caitriona Balfe as Claire Randall, a 1940s nurse who is thrown back to an earlier time after stepping into a stone circle.

"As a consultant on the show I have seen it being made, I have seen edit, and really, it has been really well done," she said.

"It is a moving story and it attends very closely to the chronology of the book."

Ms Gabaldon said she thinks the Outlander series will finish with ten books.

"I think it will be ten," she said, "but I don't plan it out, although I have a rough notion - I think there will probably be a book ten.

"Then I am planning on a sequel, which will be about Jamie Fraser's parents and the rising of the [17]15."

The prequel will tell the story, she said, of his parents Brian and Ellen, as well as his maternal uncle, Dougal MacKenzie and his godfather, Murtagh.

It will take place during the Jacibite rising of 1715, when James Francis Edward Stuart, known as the Old Pretender, attempted to seize the throne of the UK, aided by the Earl of Mar and forces in Scotland and northern England.