Sources close to the duchess said she warned her father last year that he would never meet his grandchildren.
The PM said he wants a "factual" and "evidence-based debate" about returning to free movement between Britain and Europe.
The move will take funding for the 10-year programme to more than £40bn.
The meticulously-planned visit takes in three countries in nine days - but is not without jeopardy.
Police say Mohamed Abotaka, 36, is charged with the murder of 52-year-old Ali Barzai.
Nathan Gregory says the loss of childhood sweetheart Leanne "is unimaginable for our family".