It's being dubbed the biggest wedding since Prince William and Kate Middleton tied the knot.

Kate's sister, Pippa, is set to marry banking tycoon James Matthews this weekend.

Emmeline Saunders, deputy celebrity editor of the Mirror Online, told Mike Hosking it's a BIG deal.

"It's going to cost half a million dollars, it's going to be stuffed with 350 guests from across from society, it's going to be colossal."

Actress Meghan Markle is expected to accompany Prince Harry to the wedding, at a small church in Englefield, Berkshire.

LISTEN TO THE FULL CHAT WITH EMMELINE SAUNDERS ABOVE