Middleton, 27, spent last weekend with her sister Kate and her husband at the Queen's Balmoral estate in Aberdeenshire, so they could comfort her as she deals with the split from Loudon, 31, The Daily Telegraph said.
"She and Alex split briefly in the summer but this time it's over. They are barely speaking," The Sun quoted an unnamed source as saying.
The Telegraph said Middleton's celebrity status since participating in her sister's high-profile wedding last April drove a wedge between her and Loudon.
Notable deaths of 2014 [PHOTOS]