Meet the cast of Last Tango in Halifax

Celia's daughter Caroline has had quite a time of it. In series one she's married to Tony (he's pretty awful) who is cheating on her while she is cheating on him with a woman named Kate. Also it's important to know that when Caroline meets Alan's daughter Gillian for the first time, they clash massively. Gillian thinks Caroline is a snob, Caroline thinks Gillian is insufferably cynical and moody. But slowly they start to get on and confide in each other.

In series two, Kate decides she wants a baby and Caroline eventually agrees, even though she's already got two teenage sons William and Lawrence. A guy called Greg becomes the sperm donor and Kate is about to have the baby. But in a shockingly sad episode - one of those where you have to hide behind a cushion because it's so painful - Kate dies in a car crash and her baby is delivered safely. Suddenly Caroline is a widow and a new mother in the space of a few hours. To make her life even more baffling, ex-husband and cheater John suggests they give their relationship another go. She declines. And as series three ends, Caroline is struggling with grief as she talks to Kate's 'ghost' but is absolutely in love with baby Flora, who she is now bringing up alone.

Played by: Sarah Lancashire, who you'll know as Catherine in Happy Valley, Miss Audrey in The Paradise, Raquel in Coronation Street.

Gillian (Nicola Walker)

Now, Gillian makes Caroline look like she's had a quiet life. We first meet Gillian, Alan's daughter, when she's recently been widowed by her husband Eddie. In series one, confused about life, Gillian has a one night stand with Caroline's ex-husband John, who is still involved in the family. It's all very strange- but that's the power of a few too many drinks.

John is convinced he's infatuated with Gillian but this fizzles out. Meanwhile Gillian is left looking after her grand-daughter after her teenage son Raff and his teenage girlfriend Ellie fail to care for their baby properly. And to make matters more complex, she's having a fling with Robbie, her late husband's brother.

In series three, after a turbulent romance, Robbie tells Gillian he wants to marry her but she freaks out and sleeps with John instead. Yep that John, her half-sister's ex-husband. Oh Gillian.

Cheating is definitely a theme in this show...

Despite having doubts and nearly bolting, Gillian does gets down that aisle. So when we see the couple in the Last Tango Christmas special, they're married and living together on the farm.

BUT it's crucial to know this: It's revealed in an earlier series that Eddie's death wasn't entirely an accident and that Gillian killed him after she couldn't stand him abusing her anymore. It's a pitch-black secret that has made her self-destructive, guilt-ridden and confused. And most importantly, that's partly why she felt she shouldn't marry Robbie. She's very much still dealing with the horror of what she did to Eddie in desperation.

Played by: Nicola Walker, who you'll know as Cassie in Unforgotten, Jackie in River, Sharon in Babylon, Helen in Scott & Bailey.