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The countdown is officially on!

Meghan Markle and her mother Doria Ragland arrived at the Cliveden House this afternoon after having tea with the Queen, while Prince Harry and his brother William greeted well wishers outside Windsor Castle.

The bride-to-be will hole up at the posh hotel with her mom, closest girlfriends, and her glam squad until tomorrow's ceremony. MM, wearing a Roland Mouret navy Barwick dress, told onlookers she was feeling "wonderful" about her big day on her way inside.

It was announced this morning that Prince Charles will walk his future daughter-in-law down the aisle in her father's absence, and Mr. Markle tells TMZ he's "honored and grateful" for the gesture. Thomas Markle also revealed that Meghan and Harry called him yesterday to tell him the plan, and his youngest child expressed that she loved him very much and was primarily worried about his health and recovery from heart surgery.

We can't believe it's less than 24 hours before one of the most anticipated events in history!