The Royal Engine animated TV special will see Thomas travel to London for the first time to take Sir Topham Hatt – better known as the Fat Controller – to receive an honour for distinguished service to the railway at Buckingham Palace.
Hollywood star Rosamund Pike also guest stars as a new locomotive character, the Duchess of Loughborough, for the special 22-minute episode set to air in May.
Queen Elizabeth and the Prince of Wales feature as characters in the show – with the young Prince Charles requesting Thomas’s services personally.
Harry, who recorded his on-camera introduction in January, says he grew up with the famous anthropomorphised blue steam engine, who first appeared in books in 1945.
“Thomas the Tank Engine has been a comforting, familiar face to so many families over the last 75 years – entertaining, educating and inspiring children on important issues through exciting stories and characters,” the Duke Of Sussex said.
“I certainly have fond memories of growing up with Thomas & Friends and being transported to new places through his adventures.
“I am very proud to have been asked to take part in this special episode.
“I wish Thomas & Friends a very happy anniversary.”
Pike, best known for films including Gone Girl, Pride & Prejudice and A Private War, says it is “an absolute honour” to have the chance to appear in the show.
“I take it as a big responsibility to play Duchess, who is a lovely, warm, bubbly sort of effervescent engine that I am incredibly drawn to because she is very anxious to get things right,” the star said.
Thomas the Tank Engine was created 75 years ago by British clergyman, the Reverend W Awdry, as a storybook for his young son.
That story grew to become the huge children’s franchise we know and love today, watched and read about by families in more than 230 countries and territories around the world.
The special episode will be screened in the US on Netflix on Friday 1 May and in the UK on Channel 5 Milkshake! at 9.05am Saturday 2 May.