Kate and third husband Ned Rocknroll are expecting their first child together later this year. She is also mum to daughter Mia from her marriage to Jim Threapleton and son Joe from her union with Sam Mendes.
Writing in her weekly column for The Sun, pregnant Katie sent her congratulations to Kate and said she'd been in the same situation when it comes to "backlash".
"Kate has received some media backlash like myself (for having children by three different fathers) and opinions from those, lets be honest, who don't really matter," she wrote.
"As long as you're healthy and happy I wish you all the very best for your future family."
Oscar winner Kate announced her baby news at the start of June, with a rep saying she and Ned are "thrilled" to be expanding their family. No further details such as a due date or the child's gender have been revealed.
Kate, 37, married Ned, 34, in a private ceremony in December 2012 following a summer engagement. Ned is Sir Richard Branson's nephew and currently works for his uncle's space division.
Katie, meanwhile, is currently expecting her fourth child. It will be her first with third husband Kieran Hayler, who she married in the Bahamas earlier this year.
The model is also mum to son Harvey from her relationship with Dwight Yorke, and kids Junior and Princess from her marriage to Peter Andre.