Mark Hamill nearly caught Carrie Fisher and Harrison Ford hooking up during their three-month affair.

The 60-year-old actress claimed earlier this week that she had an ''intense'' 12-week relationship with her 'Star Wars' co-star in 1976, and has revealed their fellow actor on the sci-fi series once turned up unannounced at Harrison's house while Carrie was there.

In her book, 'The Princess Diarist', she wrote: ''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.''

Carrie - who played Princess Leia in the original 'Star Wars' trilogy - revealed Harrison (Han Solo) used reverse psychology on Mark (Luke Skywalker) to avoid suspicion by joking the pair were engaged.

She added: ''It was hiding in plain sight, mocking the suggestion there was anything going on ... a technique I like to use to this day.''

Carrie has also claimed she and Harrison had ''friendly feelings and wonderful sex'', but doesn't reveal too many intimate details in her book, insisting the act of getting jiggy with it is ''private''.

She wrote: ''How could you ask such a shining specimen of a man to be satisfied with the likes of me? ... The fact is that he was!

''Sex is private. So it is with uncharacteristic reservation and scruples that I quash any details.''

Initially claiming the pair had a three-month dalliance, she said: ''It was so intense. It was Han and Leia during the week, and Carrie and Harrison during the weekend.''

Carrie has since admitted on Twitter she won't be revealing any more details about the pair's flirtation.

She wrote: ''I couldnt get twitter working on my new phone so I've been away during this out of context book excerpt time ... I would never talk about how someone was in any furniture - chair, bed, coffee table or otherwise. (sic)''