Prince William and Princess Catherine may have one of the most iconic romances in the world, but it almost NEVER wound up the way it is today! In Russell Myers' upcoming book, William and Catherine, The Monarchy's New Era: The Inside Story, he details the ultimatum that almost broke the couple up forever - and how Queen Elizabeth II and a party fixed everything! Related: Princess Catherine KNEW Prince Harry Wanted Out! In the excerpt, obtained by People on Wednesday, Myers reveals that the pressure of the high-profile romance started to weigh on Kate Middleton after several years together (they started dating around Christmas in 2003), reaching a breaking point on her 25th birthday on January 9, 2007. He writes: "With speculation over an engagement announcement at fever pitch, Catherine emerged from her London flat to a scrum of more than 20 press photographers and five television crews . . . Amid the dizzying flashes of photographers' cameras, some sprinting across the road to get in front of her, some almost stumbling over each other, Catherine struggled to get to her navy Volkswagen Polo, before the media continued to take pictures through the windows of her car as it sped away. Shaken and deeply distressed by the incident, Catherine called William in floods of tears." Aw! A source close to them said the situation and phone call were "incredibly distressing for both of them," adding: "She [Catherine] said, 'I can't do this anymore.' The situation was intolerable and William felt entirely helpless." By March of that year, things were "frosty." They'd hardly seen each other since Christmas when they met up at the Cheltenham horse racing festival. Sources said the romance had "soured beyond repair" by that point, and Catherine was "deeply unhappy and at a loss to describe how their relationship had faltered in such a short space of time." Oof. And that's when she laid out the ultimatum. Myers wrote: "Catherine delivered an ultimatum to William. A long-standing friend who she confided in at the time said, 'Catherine was distressed. She was miserable, but she certainly wasn't desperate. She felt as though she had nothing to lose and for the first time she probably relayed her true feelings to William. She wasn't demanding an engagement, but she wanted a commitment, and if he couldn't deliver that, well, then she left him in no doubt that it was best they go their separate ways.'" William was "blinded by his own insecurities" and ended up calling things off in a "30-minute phone call" in which "he laid out his reasons for believing they were on 'different pages' and said he could not offer her a guarantee of marriage." Oh, no! The author continued: "Catherine was understandably devastated. The couple agreed to give each other the space they needed. Secretly, Catherine wondered whether she would ever see William again . . . It's telling that William confided to one senior courtier that, 'at least she is free.'" Brutal. Seeing her grandson heartbroken, Her Majesty stepped in to help. Myers shared: "Sensing William was struggling, the Queen invited him to Sunday lunch to judge his mood. William was more than just crestfallen and worried about whether he was throwing away the one constant in his life. He was, according to one well-placed source, 'completely broken.' 'In that moment the Queen advised her grandson that the only certain path is the one supported by faith. It was all she had to say,' the source said." Then came a fateful party. A few months later, William "texted and asked to speak" to Kate, whose initial responses "were tentative, if a little frosty" since she was "unsure of William's motives and unwilling to let her guard down." William said he was "missing her and floated the idea of them still attending a party that had been in their [calendar] for months." Everything changed after that bash: "Reluctant to commit over the phone, Catherine said she would consider the proposal, although she did agree they should talk, if only to clear the air. Fellow guests said as soon as William and Catherine set eyes on one another it was clear their love had not extinguished. The couple peeled off from the rest of the party and spent hours locked in deep conversation. Catherine listened intently as William attempted to break the deadlock, laying out his reasons for doubting what they had. He talked of his fear of letting someone truly experience the world in which he lived, and also his fear of rejection if he did let himself get too close. Catherine, of course, knew that she still loved William deeply. That was why she had been so explicit in her demands. She was willing to agree to a future, if only he would stop allowing outside factors to affect his judgement. After speaking for what seemed like hours, William's charm, it seemed, had worked. The couple returned to the party. As the cocktails flowed and the dance floor filled, they only had eyes for each other." And the rest is history. They went on to get ma