Kate and Reese were spotted chatting for quite some time at the event in 2010, which was held in support of the The Tusk Trust, the African wildlife charity of which William is patron, and it's thought the pair struck up a bond.
And on hearing Reese had given birth to her third child, baby boy Tennessee James, Kate Middleton reportedly sent the newest member of the Witherspoon family a British themed gift.
Celebrity website Showbizspy claims Kate posted Reese a Union Jack onesie, which came complete with a handwritten note from the Duchess herself.
Just how cute?
Last week it was reported Kate Middleton had the 'baby blues' after hearing her security guard and close confidant Emma Probert was pregnant.
Although Kate's security are not normally seen, it's thought Emma has been at her side on almost every official outing, even accompanying her through St James's Park on her morning runs.
So naturally, the Duchess was thrilled when she heard the news.
'Catherine was so happy for Emma,' a source reportedly said. 'She told her she'd be the best mum and joked that she had "beaten her to it"!'
'I think Catherine was upset that she will be losing one of her closest friends just when she is needing her the most,' the insider added.
'Obviously there's meant to be a discreet distance between the Royals and their security, but they're humans, not machines.'
What do you think of Kate Middleton's baby gift to Reese Witherspoon? Super-cute? Will there be long to wait before Duchess Kate has a little one of her own? Let us know in the comments box below…