THE Queen was spotted riding p-side to visit her horses ...  she's hanging at her Sandringham estate -- where her birthday celebration rolls on.

Btw, her late husband, Prince Philip, loved Sandringham estate and the Queen as well ... she loves her ponies ... posing majestically with two of them recently -- then again, every pose is majestic by definition, right?

Prince William and Kate Middleton called her an inspiration ... just before they were seen visiting Disasters Emergency Committee HQ in London.

Speaking of Prince William and Kate, they seemed unphased by Prince Harry's explosive interview ... just hours before.

Harry sat down with Hoda Kotb on 'Today' and when Hoda asked about reuniting with his brother William and his dad Charles, the Prince deflected and never answered. It's clearly a sign of a continuing rift if not a total break in the relationships.