last spoke in person for a measly 45 minutes — and next month could be an even shorter reunion.Harry, 39, is set to return to the UK for an Invictus Games event in May. However, his cancer-stricken father’s calendar is already filling up — and fast.The monarch’s diary is “quite busy,” the Telegraph reported on Monday, and therefore any potential meeting will likely be brief.The father-son duo will be in London at the same time, as the royal redhead — who stepped down as a working royal with his wife, Meghan Markle, in 2020 — is marking the 10th anniversary of the Games at St Paul’s Cathedral on May 8.Although Charles, 75, is busy, the Telegraph reports that he will try to make time to see his youngest son if he’s able.