The Late Late Show host said the discovery of his royal ties would have grated with the republican politics of both his grandfathers.
Tubridy will allow viewers to share in his experience as he visits the historic place where his political grandparents protested British rule.
The new season of Who Do You Think You Are debuts next week with the presenter tracing his family roots which range from a remote rural schoolhouse to the place where his revolutionary grandfather was shot.
Tubridy also visited the place where his grandmother went on hunger strike.
In spite of his republican roots, during the show he discovered a connection to the very heart of the British Empire, that of the royal family.
"It sounds crazy but doing some preliminary research, I've uncovered a direct family link to Edward III. I don't want to find out anymore because I want to have the element of surprise when I'm filming the show," Ryan said in a previous interview.
"I'd loved to have seen their faces if they had found out about this while they were alive. My grandfathers on both sides would have been...very much in the republican tradition," he said.
During the filming of the show, one of his earliest research routes was in the public library in Galway where he discovered his family's Clare origins, as well the fact that his grandfather was a dispensary doctor in Lettermore. The news was discovered by viewing microfilm covering a census from 1901.
Tubridy was born and raised in Blackrock by a family closely aligned to powerful political dynasties.
His mother is a sister of Niall Andrews, the MEP, and David Andrews, the former minister whose ambitious son Barry, a lawyer, is also a TD.
His aunt Dot was a celebrated anthropologist with close links to the Kennedys, America's eternal first family, and a clan of particular fascination to the star.
Ryan is still in the midst of writing his book on John F. Kennedy's visit to Ireland in the 1960s.
RTE teased viewers with a story "from poverty and epidemics in Connemara to the seat of all wealth and power in the middle ages, Ryan Tubridy's story is full of intense contradictions."
The hit show has previously traced the family tree of other Irish celebrities such as Ardal O'Hanlon, Charlie Bird and Pamela Flood.
The upcoming season will also feature episodes dedicated to model Rosanna Davison, LOST actress Fionnuala Flanagan and actor Simon Delaney.
WHO DO YOU THINK YOU ARE? RTE 1 September 14, 9.35pm