“Meghan basically went after Kate while there was a break in the rehearsal – it was very heated and the whole Palace is talking about it.
"It started when Meghan asked Kate not to do anything to steal her thunder at the christening. Kate was pretty taken aback and said she would never do that, which only set Meghan off more.”
The insider said Meghan was also upset that Kate went to see her friend Serena Williams at Wimbledon.
“Just a lot of silly and unreasonable things, but Meghan clearly had a lot of things that she wanted to get off her chest,” the source added.
“Kate was very upset after and was visibly shaken. She knows Meghan is emotional at the moment and was taking everything out on her at the rehearsal, but it didn’t make it any easier to take.
“She tried to keep it in but ended up leaving the rehearsal in tears and Prince William had to comfort her. It was awful.”
As well as not revealing details about the event, an official Palace announcement stated that Archie's godparents would remain private too.
While newspapers are putting odds on close friends of the couple filling the roles, Phil Dampier, author of Royally Suited: Harry & Meghan in Their Own Words, tells New Idea: “The Queen is not attending but this isn’t a snub – she has engagements in Scotland and has had a busy summer.
“I’m sure William and Kate will be there and maybe one of them will be a godparent.
"That would be the best way to put rumours about a rift between the Fab Four to bed.
“But if the Sussexes just choose personal friends that will only fuel the stories!”
In fact, some royal experts fear this could be the final straw for the William and Kate.
“Harry and Meghan are obviously determined to do things their way,” Phil added.
“It’s unfortunate to say the least that they want to keep Archie’s christening private just a week after it was revealed taxpayers have spent a fortune on their new home [Frogmore Cottage].
“While the christenings of William and Kate’s children [Prince George, Princess Charlotte and Prince Louis] were not exactly public events, a camera was allowed to film the arrivals of members of the royal family and godparents on the day.
“I get the impression that Harry goes along with what Meghan wants.”
However, Mr Dampier warns that should Harry and Meghan continue to shut the public out, the consequences could be dire.
Just weeks ago, reports emerged revealing the staggering amount the new parents spent on renovating Frogmore Cottage ahead of Archie’s birth.
According to figures published from the Royal Family’s Sovereign Grant financial report, approximately $4 million in taxpayers’ money was used to refurbish Harry and Meghan’s home, which included a new staircase, fireplace and floating floor.
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