His last Tweet was on Friday, July 23, to thank a reader who had bought his latest book.
The day before he posted several photos marvelling at the moon.
But he has not posted since, not even to congratulate his daughter on her marriage to fashion businessman Mr Lewis in a stunning ceremony in Italy this weekend.
Royal fans were quick to notice Earl Spencer’s absence from the proceedings, with many questioning why he did not attend the glamourous wedding.
One person wrote: “I am tired of the Sussex drama.
“What I really want to know is why Earl Spencer was not at his daughter’s wedding”
Another asked: “Isn’t anybody curious about Earl Spencer missing his daughters wedding?”
Another person added: “Where was Earl Spencer?”
But an insider has said Charles’s absence could be due to an injury.
They told the Mail Online: “Charles recently suffered an injury and perhaps that will be the reason for him not travelling, but it is just easier for everyone that he is not there.”
In an interview with MSN last month, Earl Spencer disclosed he was suffering from a painful shoulder injury.
Explaining why he had to cancel a diving expedition linked to his bestselling book The White Ship he said: “It sounds like a pretty feeble excuse but it is really quite painful and unpleasant.
“I asked my doctor, ‘Can I dive?’ and he said, ‘Only if you want to drown’.
“I decided that would be taking the authenticity of the adventure too far.”
Lady Kitty, 30, married Mr Lewis, 62, at the Villa Aldo Brandini in Frascati with a host of socialites attending the wedding.
Guests of the couple, who had been together for two years before tying the knot, included actor Idris Elba, singer Pixie Lott and Made in Chelsea’s Mark Vandelli.
Source: EXPRESS CO UK