It's claimed the pair held secret peace talks after fearing their relationship would never heal once Harry moved to Canada.
The siblings are said to have realised it was "now or never" after Harry made the decision to step down as a senior member of the royal family.
William and Harry are said to have cut out the "toxic" people "stirring around them" to deal with things "man-to-man as brothers".
Although Harry is still said to be "at odds" with his father Prince Charles, things with his big brother are now on the mend.
A source told The Sun: "William and Harry have spent time together privately away from the official Sandringham summit working on their relationship and discussing their future."
It has been ground-breaking in terms of saving their bond as brothers and has been totally driven by them.
They added: "It has been ground-breaking in terms of saving their bond as brothers and has been totally driven by them."
Wives Meghan and Kate were also said to be involved in the peace talks "on more than one occasion".
The source added that their involvement was another sign of a "real thaw" in their relationship.
They said: "Given Harry is now permanently moving away, there was a realisation if they didn’t sort things out now, they never would. Of course there have been serious differences in opinions, but the family warmth is back. And they’re sad they’re going to be so far apart."
Harry and Meghan are now going to be spending a lot of their time in Canada, while William and his family will remain in the UK serving the Queen.
The reports came after Harry broke his silence about his decision to step back as a senior member of the royal family.
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