According to Express.co.uk the Duke and Duchess of Cambridge's first hiccup was a trial separation in 2004, while the pair were in their final year of university.
Royal author Katie Nicholl reveals how by the end of March in 2007, everyone thought their love affair had "run its course."
Nicholl goes on to reveal in her book William and Harry, how the Duchess gave her now-husband an ultimatum when pictures surfaced future king of England partying and flirting with other girls in London near his military training base at Bovington.
Nicholl wrote: “Either she had his full commitment, or they were over."
But instead of getting William's commitment, Nicholl alleges that the Prince, "Told her that they should have a break".
This is when comparisons between Kate and Camilla began, as Nicholl explains in her book: “It was hard not to draw comparisons between William and his father.
“Had William also met the right woman at the wrong time?
“Haunted by the spectre of the past, there were real fears at the Palace that Kate would become the next Camilla.”
Despite the growing concerns within the royal family, Ms Nicholl reveals that Kate had an important ally, William's grandfather Prince Philip.
Nicholl writes: “While Kate mourned the end of their relationship at home with her family, William celebrated his ‘freedom’ in London at [nightclub] Mahiki.
“While William partied, Kate received a message of support from Prince Philip.”
Nicholl alleges that the Duke of Edinburgh assured Kate that, "William will present a ring when the time is right."