Kate, 37, was at Buckingham Palace to collect her CBE, awarded earlier this year for her services to drama.
And after meeting the Queen, the Oscar winner – who has a daughter, Mia, 12, with first husband Jim Threapleton and a son, Joe, nine, with Skyfall director Sam Mendes in 2003 - disclosed that she had congratulated her and asked her about her enjoyment of acting.
Kate recalled: "I said yes I liked it but not as much as being a mother. She said, 'it is the best job'."
Not the most riveting exchange, granted, but one rooted in ordinariness nonetheless.
But are these icons of maternal majesty correct? Is it really the best job? Or the most important?
Two lesser-known but still famous-ish mums battled it out today on BBC's Radio Five Live – with very different perspectives.
In the YES Corner...TERRI DWYER, 39,
This Morning presenter, former Hollyoaks actress and former Loose Women presenter.
Mum credentials: Two sons: Caiden, six; Kylan, three
"Being a mum is hard work – I go to my other job for a day off!," Terri said. "But being a mum gives me purpose. The reason why I wanted to go to work before I had children was selfish. Now I go to work massively for them.
"To be a good mum I have to be a happy person. They are the next generation. It's maternal. If I got a job, my first instinct would be 'Great', but my next would be 'What about the kids: are they going to be OK?'
"For me, motherhood is definitely the most important job. Our children are young and we only have them for a short period time. I want to tuck them up in bed, read them stories. Can you have both?"
In the NO Corner...KATIE HOPKINS, 37,
Former Apprentice finalist, I'm a Celebrity Get Me Out of Here contestant and outspoken businesswoman
Mum Credentials: Two daughters, one son: India, eight; Poppy, seven, Max, three
"I don't believe being a mum is the hardest job or the most important," Katie said.
"The hardest job is being out there, competing in the work place, and if they are brutally honest with themselves, most mothers prefer the time they are out at work where they get intellectually stimulation.
"Clients are far harder to please than children – and you can't send a client to their bedroom at the end of the day.
"Ultimately, people feel much more fulfilled when they have a professional life, when they are competing with their peers, when they have achieved everything for themselves that they set out to achieve.
"If you can do that, then it makes you a much more aspirational role model for your children.
I don't think being at home, picking up spaghetti hoops off the floor, makes you a good role model.
"It's all well and good to be politically correct and say we were blind before our children came along, but our professional lives are what keeps people ticking.
"I love being around my children, but the happiest time is if you have a fulfilling career and then I can really enjoy the small amount of time I do get to spend with my children.
"People who spend all their time with their children, well, the tedium gets to them. Being fulfilled professionally means you can be happy spending time with your children.
"You can't be happy if you only spend all your time with your children. Mothers like me have been called a variety of not terribly pleasant names for our views, but that's the way the world works.
"There have been complaints about there not being enough women in the boardroom, but you can't be in the boardroom and then go off getting little Harry from school when he's sick."
So there you have it, conclusive proof, if proof were needed: THE best job in the world is being a mother – combined with ruling the country, living in a palace, winning Oscars, jetting all around the world, and having loads and loads of money to pay for lots and lots of servants to pick those pesky spaghetti hoops off the floor!
What do you think?