"Charlie's Angels" star Jaclyn Smith says Tanya Roberts offered her a devilish night in the bedroom ... pitching her a night of group sex shortly after Tanya joined the show.

The actress recalls the sexual offer in her new book, "I Once Knew a Guy Named Charlie: A Memoir." According to PEOPLE, she writes that Tanya and her husband -- Barry Roberts -- approached her about a threesome in 1980, before the series' final season.

Jaclyn says she wasn't offended by the offer ... instead admitting she was impressed by Tanya's "honesty about her sexuality to be brave and self-aware."

While Tanya -- who passed away in 2021 -- was a late addition to the show, fans will remember Jaclyn was an OG cast member ... making up the original Angel trio with Farrah Fawcett and Kate Jackson.

She's also the only original Angel to stay on as a main cast member for all 5 seasons ... Farrah left after just one year -- though she later returned in a guest capacity -- and Kate bowed out after 3 seasons.

Bottom line ... Jaclyn has fond memories of being an on-screen threesome -- but that threesome never made the move to the bedroom.