Kate isn't the only woman to discover the advantages of friendship with an older woman. In recent months Stella McCartney has grown closer to Marianne Faithfull who not only understands her lifestyle but, at 51, could be counted as a mother figure for the bereaved 27-year-old.
Meanwhile 26-year-old Geri Haliwell, the less-than-secure ex-Spice Girl, has found Dawn French (41) a source of solace. (She apparently agreed to do Comic Relief after French suggested it might cheer her up.) Kate Winslet (24) has remained buddies with Emma Thompson (40) since they worked together on Sense and Sensibility. And 33-year-old Elizabeth Hurley was seen bonding with Joan Collins, who is 66, at a Valentino launch earlier his month.
Indeed the generation-gap friendship has become so sexy that it has inspired Donna Karan's latest advertising push. For her Spring/Summer campaign, Peter Lindbergh photographed supermodel Annie Morton leaning towards a sixty-something model as if she'd find succour in her silk-clad shoulders.
There is good reason for a woman to make friends with someone who was raising hell when she was still teething. Women like Pallenberg and Faithfull know all about fame, fortune and failed relationships. They are can relate to this generation of younger women's lives because they were the people who pioneered sexual freedom and made the tough decisions that came with it. They blazed a trail through the Rolling Stones, paid the price of free love and survived Rock Chick Hell. Whether Anita and Marianne still play hard or not, who better to advise Kate and Stella on the pitfalls of sex, the downside of drugs and the rigours of rock'n'roll?
Of course, not all of us have a Pallenberg or a Faithfull to turn to, but increasingly women in their twenties and thirties are searching out a "life mentor" - someone who gives advice like a mother but reacts like a friend, precisely because they have been there themselves.
So why are women turning to older friends? First there's the absent mother factor. Most of us have moved away from the family home and there are times when a long-distance phone call just isn't enough. And while friends our own age can be a great comfort in that "we're-all-in-it-together" way, older women can put problems into a perspective. What we regard as a catastrophe can appear a mere blip to a woman who has had 20 years more life experience.
Then there's that feeling of pride that holds us back from discussing disasters with our peers. "Many of my friends are in their mid-thirties like me," explains product designer Karina Johnson. "We share our problems to a certain extent, but if I feel like I've done something really stupid I'll turn to Terri for a shoulder to cry on."
Terri is 65, and for Karina she's a cross between a surrogate mum and a good-time girl. "I can go out with her, have a few bottles of wine and go home plastered," she says. "But I also know that if I want to confide in her, she won't judge me or have that slight competitive thing going on. With friends of my own age, there's that feeling they're thinking `Oh, I'd never have done that' or `God, she'll never grow up', because that's exactly how I think about them. We can't help competing with each other."
An older friend is the best of both worlds: a mentor and a mate. I've been friends with 61-year-old Yvonne for six years. I first met her at a dinner party given by a mutual friend, and she'd been given the sort of build-up normally reserved for the Queen Mother. I found her bossy and nosy with piercing blue eyes that seemed to see right through you. I was unnerved to say the least.
I gave her wide berth until I realised how easy-going she was. She turned up to a mutual friend's lunchtime party not long after our first meeting, got drunk and ogled the rugby players on the telly. She was always inviting a pack of thirtysomething friends over for dinner and it wasn't long before I became her latest recruit. Since then I've been provided with the sort of entertainment last seen in the best bits of Abigail's Party.
But it wasn't until my mother became very ill that I realised her nosiness was really concern. She had similar problems but she'd always ask about mine first, which was rather a new concept. I suppose she has become more of a surrogate mother as my own become more fragile. When the family home went up for sale and my mother moved into a home, she told me what a good thing this was, how it would give me a new-found freedom. In all the time I've known her, she's never been negative.
Many times I've sat opposite her, squirming, as she asks me whether I've started looking for a new flat, sorted out my relationships and generally taken control of my life. She makes me face things that my peers aren't interested in. She doesn't mince words or cut a swathe through my ambitions and she doesn't let me get away with giving her namby-pamby excuses if I don't do the right thing. Equally, she'll hit the nail on the head while I'm banging mine against the wall.
She always lightens a problem with some story of a friend who did something worse in 1974 and came out unscathed. And there's something rather comforting in knowing a sixtysomething who still has a lust for life rarely matched by work-weary ambitious younger friends.
So what does she get out of it? "I get a lot more than I give," she says. "It's quite a privilege to share someone younger's life. You tend to get a bit stale as you get older, and looking at another view of the world keeps you young.
"It's not a surrogate mother thing. I'm interested in what young people are doing - especially when you can see exactly what's going on for them. Life is more difficult for young people now because there is more freedom of choice and that is a huge responsibility. Freedom is fine if you can handle it properly."
Yvonne is one of a new breed who refuse to conform to how a sixtysomething woman should behave. "I don't act 61, I don't look 61," she says. "It's just a date on a piece of paper. I think that when you're single and my age, you've got it made as long as you've got the right attitude."
Another friend, Elizabeth Colbert, 65, agrees. "I have a lot of friends who are younger than I am," she says. She believes it's made a big difference that hers was the first generation of women who had careers long term."I think many women of my age have a younger outlook than they had 10 years ago," she says.
"I've worked with people of all ages, tastes and lifestyles and that gives you a greater degree of flexibility with younger people. Women in their sixties used to be the matriarchs, the grandmothers who lorded it over the family. Now society has become much more mobile. People are generally younger for their age and we're all so much more active that it's no surprise we have younger friends. In my friendships with younger women I'm not acting just as an agony aunt. It's much more fun than that."
Perhaps these older women are our new role models in more ways than one. As fewer women opt for motherhood, becoming a friend and confidante to younger women might be a more realistic ambition. Either way let's hope that, like them, we'll have some decent advice to impart.