“Things were already tense between the brothers when Harry met Meghan, but things became much, much worse after they got married," the insider told The Sun.
"Harry and Meghan didn’t spend any time with William and Kate, and the two wives don’t get along at all – the distance and the differences between them grew into a vast chasm.
"William and Kate are far more formal and easily fall in step with royal protocol, Harry and Meghan went in the opposite direction – they have nothing in common."
The source continued: “Similarly, Harry began spending less and less time with his old, lifelong friends, he stopped being the laddish, relaxed character he had been, he became more private and withdrawn. Nobody can blame Harry for wanting to protect his wife, who has had a very tough time with the British press.
"Harry absolutely loves her and wants her to be happy and safe, and more importantly not suffer as his mother Diana did. But now all Harry’s friends now seem to be Meghan’s Hollywood friends, like the Clooneys."
“It is almost as if she has taken total control of his life,” the source speculated.
When it comes to the couple's shock decision to quit their duties as senior members of the royal family, the insider said that Meghan was the driving force behind it.
“Everyone is convinced Meghan is the driving force behind this move to quit the royal family," they told the publication.
"She is the one who most wants to be back living in Canada and California, where she feels happy, and to bring their son Archie up away from the restrictive and intrusive politics of Buckingham Palace.”
The unexpected decision to quit took the world by surprise, and was announced on their Instagram on Wednesday.
In a statement they said: "After many months of reflection and internal discussions, we have chosen to make a transition this year in starting to carve out a progressive new role within this institution."
They continued: "We intend to step back as 'senior' members of the Royal Family and work to become financially independent, while continuing to fully support Her Majesty The Queen. It is with your encouragement, particularly over the last few years, that we feel prepared to make this adjustment.
"We now plan to balance our time between the United Kingdom and North America, continuing to honour our duty to The Queen, the Commonwealth, and our patronages. This geographic balance will enable us to raise our son with an appreciation for the royal tradition into which he was born, while also providing our family with the space to focus on the next chapter, including the launch of our new charitable entity.
"We look forward to sharing the full details of this exciting next step in due course, as we continue to collaborate with Her Majesty The Queen, The Prince of Wales, The Duke of Cambridge and all relevant parties. Until then, please accept our deepest thanks for your continued support."