After nine years of marriage, one daughter and years of enforced separation caused by relentless touring with his band 10cc, Eric Stewart's wife Gloria started complaining that he no longer told her he loved her.
Her grumbling fell on deaf ears. "If I said it all the time, it would lose its meaning," he would protest. Which, to Gloria, felt a little thin.
After all, when they'd met - at one of his gigs at Halifax Town Hall in 1964 - he'd been poleaxed by the beautiful 16-year-old. ("I went gaga! Completely gaga!" he says today.)
But, then, Eric thought again. Even better, he secretly wrote an ironic song explaining exactly how deeply he adored her, how desperately he pined for her when he was away, how he hung her picture on his wall and gazed at it - all without using those three little words.
Eric wanted to write a love song for his wife without saying "I love you". He wanted to show the conflict between feeling a certain way, yet avoiding those words.
The result, I'm Not In Love, was a massive hit in 1975, going to No 1 in charts all around the world; it earned endless royalties and inspired an entire generation of musicians.
Everyone over the age of 40 knows the lyrics "I'm not in love, so don't forget it; it's just a silly phase I'm going through".
The song has been the soundtrack to countless romantic moments. It also made Eric and fellow Mancunian band members, Graham Gouldman (who co-wrote the song), Kevin Godley and Lol Creme, very rich. Even more important, it placated the lovely Gloria. Earlier this month, they celebrated their 52nd wedding anniversary with a big dinner for friends.
"We try to be romantic - we send each other cards and flowers and surprise each other. It's important to keep that side going," says Gloria, who is still a vision, with blonde hair, pink cheeks and great legs. "Even if sometimes someone needs a bit of a reminder..."
Eric is more prosaic. "The fact it's lasted 52 years, especially in the music business is bloody astounding," he says. "Because you're tempted all the time!"
Now 73, he looks more like a rather meek music teacher than a rock star who has worked with all the greats, from Paul McCartney to the Rolling Stones, Stevie Wonder to James Brown.
As he offers me a flapjack, it's easy to forget that, in the halcyon days of the mid-Seventies, 10cc - christened in 1972 by record producer Jonathan King (later convicted of child sex abuse) who signed them to his label and then had a dream about a chart-topping band under that name - were the most popular group in the world for a time.
That night he met Gloria in 1964, Eric, a 19-year-old self-taught guitarist, was well established on the music scene. His band, Wayne Fontana & the Mindbenders, was riding the wave of their first major hit, and was a popular live attraction throughout the UK
Ignoring her father's gruff "I'll give it two years", she became wife to one of the biggest pop stars in the world at just 18. On their wedding day, March 10, 1966, the Mindbenders (without Wayne Fontana) were back at No 2 with A Groovy Kind Of Love.