Michael Douglas' family tree extends far beyond his wife Catherine Zeta-Jones and his three children, thanks to his first wife, Diandra Luker.
In 1977, the actor, now 80, married Diandra, the daughter of an Austrian diplomat. They welcomed son Cameron Douglas, now 45, together, who is an actor just like his dad.
Diandra, 68, is also a mom to three other children, sharing twins Hawk Paxton de Morrell Bacon and Hudson Hunter de Morrell Bacon, 20, with her ex-fiancé Zach Bacon III, plus her adoptive daughter Imara de Morrell Douglas, who bears the famous family's last name.
Cameron took to social media to mark his younger half-sister's 19th birthday, with Imara serving as the youngest in the line of Douglas siblings. Michael and Catherine share children Dylan Douglas, 24, and Carys Douglas, 21.
"Happy Birthday angel," he simply wrote alongside a sweet throwback of the pair sitting beside each other, with Imara definitely looking like her mom Diandra's twin.
Michael and Diandra were married from 1977 to 1995. Their love story was a quick one, having first met when Diandra was a 19-year-old student and Michael was 32. They began dating and two weeks later, Michael proposed. And just six weeks after that, they were hitched.
They welcomed their son Cameron a year after tying the knot and remained together for nearly two decades before splitting up. The Wall Street star and the Chicago actress got married in 2000.
Looking back on their split, Michael told The Mirror: "I know I'm going to get into trouble here. I have nothing against her and in fact I'm very fond of my first wife. But we should have ended that marriage eight or 10 years earlier."
"It took me too long to [realize] that if you go to a marriage [counselor] to resolve problems, it's in his interest to keep the marriage going," he added. "Because if I end the marriage he's got no business. I think Diandra would probably say the same thing. That's the only clear regret that I have."
MORE: Michael Douglas' son Cameron reacts to younger brother Dylan's dashing appearance in new photos
Their divorce resulted in one of the most expensive celebrity divorce settlements ever, a reported $45 million, plus the tense distribution of their assets, and a drawn-out court case in 2010 when Diandra filed to receive part of the earnings from the movie Wall Street: Money Never Sleeps in 2010 as a producer.
"I loved Michael very much when I married him," Diandra told Harper's Bazaar in the midst of their trial, which also centered around their Mallorca vacation home which Michael now shares solo with Catherine.
"And I don't think love ever really disappears. It might metamorphose, [but] I certainly don't think that hate is the right recipe," she continued, stating that she hadn't actually met his new wife at the time. "I'm really happy that he is madly in love and has two lovely children."
The relationship between the children is certainly warm, however, as Cameron maintains a close bond with his half-siblings Dylan and Carys, as well as Imara, Hawk and Hudson. He himself is also a dad-of-two with longtime girlfriend Vivien Thibes.