Much like her That Girl alter ego, Ann Marie, a young and prescient Marlo Thomas knew about "Girl Power" long before the Spice Girls hit the scene.

"I remember thinking at a very early age, 'I'm always going to know where I'm going,'" she says in a Lifetime Intimate Portrait airing tonight (7 pm/ET). "Nobody's ever going to say to me 'What does she know? Where is she going to go?'"

As the single-minded daughter of legendary entertainer Danny Thomas and a junior member of Hollywood royalty, where Thomas went was straight into the family business. And in the early '60s — buoyed by a breakout performance in the London stage production of Barefoot in the Park — television beckoned.

"The head of ABC at the time called me in and, just like the old story, said 'Kid, you can be a TV star. I'm gonna find a series for you.'" Unfortunately, he didn't have a concept — but Thomas did. "There [was] all this stuff happening in the country with women, [yet] everybody on television is either the daughter of somebody, the wife of somebody or the secretary of somebody. [I said], 'Why don't you just do a show where the girl is the somebody?'"

Thus, That Girl was born. The series, which ran from 1966-71, was immensely popular — a fact Thomas attributes in large part to the late Ted Bessell, who played her on-screen comic and romantic foil Don Hollinger. "Half the show was Teddy," she says. "There was no show without [him]."

Even off-screen, Bessell made quite an impression. "[We] definitely had a romance," Thomas admits. "I was crazy about him. Every girl wanted to go to bed with Teddy. He had all the male stuff."