Mark Hamill says he was "blissfully unaware" that Carrie Fisher and Harrison Ford were having an affair on the set of 'Star Wars: Episode IV - A New Hope'.

Mark Hamill

Mark Hamill

The actress - who played Princess Leia - finally confirmed romance rumours that surrounded the pair when she published her memoir 'The Princess Diarist' last month which details entries in her diary from 40 years ago and included writings on her three-month romance with Harrison when she was 18 and they were shooting the movie in London in 1976 and the then-33-year-old actor was married to Mary Marquardt.

Mark - who portrayed would-be Jedi Knight Luke Skywalker - was close with both Carrie and Han Solo star Harrison but never noticed that they were anything more than just friends in a galaxy far, far away.

Speaking to 'Entertainment Tonight', the 65-year-old actor said: "I was blissfully unaware ... I was so self-involved at that point, they could've been doing it in front of me and I wouldn't have noticed. I was single and had my own agenda ... I think it might have been a distraction if I'd known what was going on."

Mark - who reunited with Carrie and Harrison for 2015 'Star Wars' film 'The Force Awakens' - admits on-set romances are quite "commonplace" but often end in awkwardness for those involved and the rest of the cast.

And the sci-fi star knows from first-hand experience because it happened to him when he had a short-lived relationship with his 'General Hospital' co-star Anne Wyndham in the early 1970s.

Mark - who has been married to his wife Marilou since 1978 - shared: "If the relationship doesn't last and you're on a TV series and you got four more seasons to go, it can be really awkward. It happened to me. I was with a girl who was playing my sister on a soap opera, 'General Hospital'."

In her book, Carrie, 60, spills that Mark almost caught her and Harrison, 74, in the act when he turned up unannounced at Harrison's apartment when she was there for sex.

She writes: "Once, on one of the rare occasions when we did have a sleepover at Harrison's apartment, Mark ... dropped by unannounced. Clearly I hadn't just dropped by for brunch."