The model – who is currently pregnant herself – reached out to Peter and Emily via Twitter on Monday afternoon (22 July).
Katie wrote: "Genuine congratulations to Pete and Emily and I hope they are very happy."
The 35-year-old - who divorced Peter in 2009 - added that the kids are "excited" about the new arrival.
Katie and Peter are parents to son Junior, 8, and daughter Princess, 6, while Katie also has an 11-year-old son, Harvey, from her relationship with Dwight Yorke.
Genuine congratulations to Pete and Emily and I hope they are very happy – kids excited xxx— Katie Price (@MissKatiePrice) July 22, 2013
A rep for Peter confirmed Emily's pregnancy to Reveal this morning, saying the couple are "over the moon" to be starting a family together.
They have been together for around a year, but met back in 2010 when Emily's father performed surgery on Peter.
Katie, meanwhile, is expecting her first child with third husband Kieran Hayler. They married in The Bahamas in January following a whirlwind romance, and announced their baby news a few weeks later.
Shortly after their wedding, Katie released a statement that included a reference to 23-year-old medical student Emily.
She said: "I wish Pete nothing but love and luck with his relationship with Emily who seems delightful."
Katie and Emily aren't the only pregnant stars - check out our gallery below:
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