It is rather funny, considering she never got engaged to the chap (when the negocciations failed the dutch ambassador to London, who had to arrange the thing, was taken ill to bed for two weeks). In Holland people were however akmost certain about the engagement, photographs were placed in shopwindows, songs like these were made and small books/articles were written about Carl (who is the brother of Crownprincess Martha of Norway and Queen Astrid of the Belgians). The funny thing about the song is that it already is wrning Juliana, not to let the guy slip, which was exactly what she did. Note that the song affectionally refers to 'Juliaantje' as if they were referring to family, I remember my grandmother usually calling her that way as well.
I believe Wilhelmina blamed it on a danish/norwegian/greek conspiracy, headed by Queen Maud of Norway. At other times the belgian King and Queen were suspected, because they wanted the younger brother of the King Prince Karel) to marry Juliana.
In reality Carl didn't care much for Juliana and Juliana didn't care the least for him (she found him to childish, and even according to the dutch ambassador in Sweden, the swedish princes were only interested in cars, parties and women) but for Peter of Greece, who was unsuitable as his great-grandfather owned a casino in Monte Carlo. The dutch ambassador to London later even admitted that Juliana went out of her ways to behave aloof and haughty to the swedish Prince. I wonder if she later on regretted on her decission...