The London and Seattle-based practice has admitted that the recent war had left hopes for the project - which was on site - in tatters.
The project's designs aimed to become a visual symbol of the Lebanese capital's 'cultural pluralism and rich shared history'.
While the site itself was unharmed by bombs, Katherine Gustafson, the creative force behind the Diana Memorial Fountain, admitted that the scheme was now unlikely to go ahead.
Beirut redevelopment agency Solidere had begun the painstaking construction in 2003, she said, and many of the enclosing walls are complete.
'But now,' she said, 'everything's stopped. It hurts. This is one of the most moving projects I have ever worked on.
'One park will not change the world, but you might change a nanosecond of someone's thinking, and that accumulates,' she added.
Lebanon conflict destroys Garden of Forgiveness plans