The hedge fund manager and brother of Made in Chelsea star Spencer Matthews surprised Pippa by popping the question during a romantic weekend away in the Lake District.
But as the jaw-droppingly stunning bridesmaid for one of the most iconic weddings ever, her sister the Duchess of Cambridge and Prince William, everyone's now wondering - will Kate return the favour for her sister's wedding, due to take place next year?
There's already been lots of speculation about the 2017 wedding, but some of the biggest theories concern Kate Middleton donning a bridesmaid title for the celebration.
It is unusual for royalty to take on this kind of role, but Wills and Kate are the most modern monarchy yet, so perhaps they will break tradition?
Royal expert Jennie Bond exclusively told OK! magazine her views on the matter, leaning towards the opinion that Kate may break tradition for her sister. 'I'm sure Kate will want to be a bridesmaid, as her and Pippa are so close. I really do hope they break tradition.
Pippa and James are due to marry next year!
'From what I know of Kate, she is a decent, loving sister and she'll want to make absolutely sure it's very much Pippa's big day, so she will want to cling to normality - but that's hard when you're the Duchess of Cambridge!'
However, Royal writer Judy Wade has a very different outlook for the nuptials next year.
In an interview with People magazine, she explained that Kate may feel more comfortable in the background, so as not to draw all of Pippa's big day attention away. 'She would want her sister by her side, as who else would she trust to make things go well?
Pippa was Kate's bridesmaid on her big day on 29th April 2011
'But if your sister is a future Queen, she is going to upstage the bride and draw attention. Kate would want to be in the background as much as possible.'
It's also rumoured that instead of opting for the white that Kate chose for Pippa's dress on her big day, Pippa may instead go for pastel colours, which we think Kate would look lovely in!