And even now as they've both entered the stage of motherhood, that hasn't changed.
Cotton, who is expecting her second child with Jesse Wood, wore a dress that flattered her growing baby bump and held Willoughby's hand as they headed to ITV's annual summer party together this week.
The famous mum has decided not to find out the gender of the baby and has not yet revealed her due date.
Her pregnancy style worked well during the heat, as she donned an airy tie dye dress with blue heels to match and a bright purple bag.
Cotton announced she was expecting her second child in February this year.
She and her husband have a two-year-old son, Rex together.
Opening up about her friendship with Willoughby in a recent interview with Red magazine, Cotton gushed about how she idolised her pal still after all these years.
She told Red magazine: "My aim in life is to be grown up like Holly. I go round there and her house is so perfect and she's so together and I go home and I think I live in a s**t hole!"
Cotton has previously spoken about how she felt becoming a mother for the first time in 2013.
She told The Express: "When I had my son Rex two years ago, I don’t think I was expecting anything to change, but the love that you feel is off the scale."
During the annual ITV party, Willoughby, 34, opted for a plain black dress with simple pointed black heels.
She is still on maternity leave after welcoming her third child with husband Dan Baldwin, who have Harry, five, Belle, four, and nine-month-old Chester.
Soon returning to This Morning, fans have expressed their excitement at seeing her back on TV again.