This is why Toni Tennille really left 'the Captain' ...

Fans were shocked after news broke in 2014 that '70s musical duo Captain & Tennille were splitting after 39 years of marriage.

Toni Tennille, as she revealed in her tell-all memoir, was also stunned that hubby Daryl Dragon, aka the Captain, posted the news through a cryptic announcement on their website.

After numerous rumours that Tennille was gay and "had a girlfriend for years", her memoir digs deep into her marriage with Dragon.

According to the book, their marriage was rocky from the beginning.

Dragon was reportedly quirky, controlling and distant, and was unable to return his wife’s affections (the couple always maintained separate bedrooms).

Though Tennille insists she never cheated on her husband — despite being trapped in the loveless and "lonely" marriage for nearly 40 years.

The singer reveals that A&M Records basically forced the duo into marriage in 1975 by issuing a press release saying that they had wed on Valentine’s Day.

"Of course they neglected to say anything to us about it," she writes.

"So it wasn’t until fans began mentioning it in their letters that we learned our record label had 'married' us."

Their real wedding took place a few months later a tiny chapel at the Silver Queen Saloon in Virginia City, Nevada.

"I don’t want Daryl to be blamed for anything," she says.

"A lot of things that happened in my life are because I wanted him to be something that he couldn’t be. That’s on me."

"I can’t blame Daryl; I blame myself. He just couldn’t be what I’d dreamed he could be."

She is now content to spend the rest of her life alone.

"I think that is kind of late to go looking for somebody else.  Besides, even though Daryl and I were together all those years, I was kind of on my own and lonely for a long time."

Dragon passed in January this year from kidney failure at the age of 76. Tennille was by his side.