The Royal Foetus
Here is a modular poem. below, I have appended various options for the third and fourth lines, which you can select according to taste (or lack thereof)
The Royal pair have feasted on sprout.
It's had an effect, without doubt.
Because she's got one up the spout.*
* this line might need slight tweaking depending on which of the following missing lines you opt for.
Options for third and fourth lines
A: The result of their f***ing
Is that Kate is up-chucking
B: This royal fornication
has delighted the nation
C: Because those sprouts from Brussels
Sustained William's muscles
D: Pippa's next book, in future
Is the royal Karma Sutra
E: Because the Royal Willy
Has covered the filly