Buckingham Palace staff are said to be "sweating" over the lack of details about Prince Harry 's trip to the UK this weekend.
The Duke of Sussex confirmed he will attend the King's Coronation on May 6 and that his wife Meghan Markle will remain in the US to celebrate their son Archie's fourth birthday.
It has been reported that Harry's trip to the UK will be short as he is expected to leave shortly after the Coronation to join his family in California for the birthday celebrations.
Last month, a royal source told The Mirror : "After much back and forth, Harry said that he would be returning for the King's Coronation but it will only be a fleeting visit.
"Organisers have been told Harry won't be attending the concert with the rest of the Royal Family, which is a great shame as it will be such a spectacular event."
But a source has now claimed that some people involved in the organisation of the Coronation are "not quite so convinced" that Harry will actually attend it.
However, they said that the "working assumption" is that he could arrive as late as Saturday morning by private jet and leave that same afternoon so that he can return home in time to celebrate Archie's birthday.
The insider added Harry is "making everyone sweat about his movements", with officials still seeking confirmation of "when he is coming, where he is staying, when he is going back and whether he is happy with his seating position in the Abbey."
The anonymous source told the Mail on Sunday : "Harry seems to be adopting a High Noon approach, making everyone sweat about his movements.
"While the Royals are confident that he will show up, others involved are not quite so convinced.
"The working assumption now is that, assuming he does come, it could mean arriving as late as very early Saturday by private jet and leaving by late afternoon the same day."
The claims come as royal biographer Tina Brown said the relationship between Harry and his brother Prince William is " on absolute ice" ahead of the Coronation.
She said she doubts there will be any reconciliation between the two brothers who appear to be "totally estranged".
Ms Brown told LBC's Andrew Marr: "They are totally estranged. I do not think there will be any contact between them at the Coronation. I think that their relationship right now is on absolute ice.
"The longer Harry dwells on what happened in his life, the more he feels resentment against William, because he feels, I think, that William was even more calculated, essentially, in making him number two, making him the spare, and feel like the spare at all times.
"So, there's no contact between them, I'm told. I think Charles wants to have some kind of rapprochement. But I think it's going to take years… It never happened between George VI and the Duke of Windsor, it just got worse.
"Alienations tend to get worse as time goes by, rather than better."
