Divorce, they say, is hardest on the kids. But putting the children first when you're embroiled in the hurt, betrayal and insanity of a long-term break-up, is even harder when they're not biologically yours.
Jim Carrey was criticised on national radio in by his former long-term girlfriend Jenny McCarthy for losing contact with her son. The model and actress, with whom Carrey split in 2010, claims Evan, 10, who suffers from autism, has been in therapy to cope with separation from his former stepfather Carrey, who has denied that McCarthy directly invited him to stay in touch with the boy.
Step-parenting is a tricky business under even the most Brady Bunch of circumstances. But when a relationship goes awry, how best to attend to the needs of a child who has probably depended on you and been told to love you, but who is not your flesh and blood, and to whom you have no legal obligations after a split, is a minefield.
It can take years to "blend" families; with children belonging to different partners, grown-up offspring, new babies and the grandparents, aunties and uncles that come with them. Difficulties between parents and children who are not related by blood are among the key causes of relationship breakdowns. But when this happens (and assuming the adults don't then declare themselves celibate), the complications seem to perpetuate themselves. Divorce rates among those already divorced have been consistently high for the last decade. Nearly 40 per cent of marriage dissolutions in England and Wales annually occur between couples where one partner has been married before. More than 9 per cent of divorces each year happen between couples who have both been married already.
"What the marriage and divorce statistics don't take into account is the high number of co-habiting couples who then split up," says Christine Northam, of Relate. "Children grieve for the loss of their home as they know it. Parents need to be very mindful of what they are doing."
A child's natural loyalty to a biological parent who has been replaced by a new spouse is just one of the many complicated problems that can influence daily lives in a step household. The arrival of new children who might have to suddenly share rooms, toys and attention will undoubtedly upset the order of things – and can produce tension. Parents who have done it will tell you it takes the resilience, stamina and patience of a saint to create a functional step-family. But if, having got there, and "blended" into being, however unconventional, ragbag and surprising your family is, if the whole thing breaks down once again, it can be unendurable for children. Lizzie, 38, grew up in her father's care after her parents divorced. He married his secretary after a work affair and Lizzie and her younger sister and brother moved in with the woman who caused the end of her parents' marriage. Two half-brothers soon arrived.
"There are 15 years between me and my youngest half-brother, so people thought he was mine," she says. "My stepmother was out working a lot so I looked after the little ones, which I loved." Despite the bonds between the siblings, coping with her father's "new family" brought with it an additional set of emotional ramifications. "Being part of the first set of children does make you feel you were never good enough," she says. "You feel misplaced. I am biased but I think for men, children from previous marriages come last. It's different for mothers."
Having got over initial feelings of resentment towards her first stepmother (over her father's infidelity), Lizzie was stunned when her father left his second wife for a younger woman. Lizzie didn't keep in touch with her first stepmother and couldn't form a relationship with her father's third wife.
Mary, 37, a journalist, has a more positive view of the break-up of her blended family. Her parents divorced when she was 14 and both remarried. Her mother's new husband had two sons who came to live with them, the youngest of whom was a similar age to Mary. "We became brother and sister really quickly," she says. "His father cheated on my mother about 10 years later so I didn't stay in touch with my stepfather, partly because I didn't want to for Mum's sake, but also because he didn't want to have anything to do with me. But my brother made a real effort to maintain the relationship with us." Strictly speaking they're not related in any way but they still refer to each other as brother and sister "because it would be weird not to".
It's easy to focus on the negative sides of melded families gone wrong. But often, as in Mary's case, even if the "unit" breaks up, positive relationships endure. Interior designer Kelly Hoppen is stepmum to the actress Sienna Miller, despite having divorced her father years ago. They appear at glitzy events together, Sienna having recently supported the launch of stepsister Natasha Corrett's new cookery book, and Hoppen publicly confirmed Miller's pregnancy earlier this year.
Pop singer Peter Andre and model Katie Price divorced in 2009 after four and half years of marriage. They have a son and daughter together and Andre has been vocal about his continued relationship with Price's disabled eldest son, Harvey, 10, whom she had by footballer Dwight Yorke. Andre dedicated 2010 single "Unconditional" to Harvey and has paid money into a trust fund for the boy. And the actress Demi Moore's daughter, Rumer, appears to be feeling her way towards a continuing relationship with her former stepfather, Ashton Kutcher, to whom she was very close when he was married to her mother, despite the difficult nature of the break-up.
Northam warns against underestimating the impact a step-parent may have had on a child's life. "I would always recommend, if possible, maintaining a relationship with a child, even if it's limited to a cup of tea every so often," she says. "Parents and step-parents need to be as honest as they can with their families. Don't shroud it all in mystery. Give children age-appropriate information. If you can do it together that can be very helpful because it shows the child you can co-operate on their behalf."