Rod Stewart ''should have known better'' than to marry Rachel Hunter because she was ''far too young'' to tie the knot with him.

The rocker admits his former wife - who he wed in 1990 before separating from in 1999 - broke his heart but he always knew she would because in the end their age difference proved to be too much for their relationship.

Model Rachel met Rod when she was just 21 and he was 45, an age gap of 24 years, and they had children Renee and Liam together before eventually divorcing in November 2006, seven years after their initial split.

Speaking about their union, Rod, now 70, said: ''Rachel broke my heart. Obviously we're the best of friends now because we've got two kids together. I married Rachel when she was too young. I should have known better. At the wedding ceremony, my sister said to my brother, 'She's gonna break his heart some day,' and she did.

''No fault of hers, I should have known better, she was far too young to have got married.

''That's been the only one so far and she was quite right, she was living in my shadow, she hadn't done enough growing, it just took her a few years to admit it, it was seriously heartbreaking.''

The pair's separation came shortly before Rod had a two-week run of concerts and he spent each night expecting her to turn up for the shows.

He admitted: ''I kept looking at the side of the stage hoping she'd come to a show and she never did.''

Rod has been married to Penny Lancaster since June 2007 and they have two sons, Alastair, nine, and Aiden, four, together.