These 'visits' by English Kings were often uninvited and unwanted (Henry I, Henry II, Edward III and Henry V being prime examples), and their frequency is easily explained by a number of factors, not least of which is that they held territories in France, and usually wanted more. However, not all these English visits were hostile: Richard II and Edward II (while kings) went there to get married, Harold II (before he became king) was shipwrecked, Edward I passed through on his way to and from the Holy Land.
Visits by French Kings to England (within the British Isles) were much less common - I've only found 4 (out of more than 30, starting with the Capetian Dynasty) for the entire medieval, early modern and modern periods: Louis VIII, John II, Louis XVIII and Charles X. There are several reasons for this, not least because they did not have any territories in England (that I know of). Of these, the only reigning monarch was John II, and he did not make the trip of his own free will: he was imprisoned in London during the Hundred Years War after being captured at the Battle of Poitiers in 1356. Earlier, Louis VIII had led an abortive invasion of England during the reign of King John in 1216-17, but this was before he became king. The only other 'visitors' I've found are in the modern period, two of the exiled Bourbons who were later crowned Louis XVIII and Charles X.
Aside from the aforementioned monarchs, did any French kings ever set foot in England or any other part of the British Isles (either before or after becoming king)? Although I'm primarily interested in the medieval period, other answers would be of interest.
Note: For the purposes of this question, Henry VI of England doesn't count as a French King.