The duchess, who is about seven months pregnant with her third child, is set to open the centre in Wickford, Essex, this afternoon.
The royal appeared to get stuck in a drain grate as she when to greet charity staff and council officials.
Kate, 36, has been a patron for the charity, which also offers life-saving treatment to individuals and their families in London and Wiltshire, since 2012.
The pregnant duchess looked blooming lovely in a royal blue Ellory bow coat by Goat, black tights and heels.
Today, she will learn more about the organisation’s community-based recovery programme, Clouds in the Community.
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As she arrived, Kate waved to the crowds of royal fans, carrying gifts and flowers, who had gathered in the cold to catch a glimpse of the Duchess.
The Vice Lord Lieutenant of Essex, Jonathan Douglas Hughes, who appeared to fall ‘head-over-heels’ for the Duchess in 2016 was there again to greet Kate as stepped out of a black Land Rover near the new treatment centre.
The pair shook hands and seemed to share a joke as the Duchess let out a small laugh.
The Vice Lord Lieutenant made headlines after took a tumble when Kate accompanied by Prince William visited an Essex secondary school to promote their Heads Together campaign two years ago.
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As the couple arrived, the Vice Lord Lieutenant of Essex, Jonathan Douglas Hughes, who was outside to greet the couple, fell backwards with a dramatic thud.
The waiting crowds gasped in shock at the sight as he struggled to get his feet.
Fortunately William - who was a part-time pilot with East Anglia Air Ambulance - rushed to his aid and helped the embarrassed and slightly shaken man to his feet.
In 2015, Kate visited Wiltshire where she told graduates: "It’s such a positive story for you all."
Clouds in the Community aims to offer an effective alternative to residential treatment and provides the charity with an opportunity to provide services in more than one place.
While there, Kate will take part in a round-table discussion with healthcare professionals, staff and clients, and attend an opening reception.
The charity also offers educational courses up to degree level at The Centre of Addiction Treatment Studies in Wiltshire.
The centre works in partnership with the University of Bath to train addiction counsellors.
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The pregnant duchess has already been very busy at the start of this year, having just got back from a four-day Nordic tour in Sweden and Norway.
The charity has several sites around the country, including its flagship Clouds House centre in Wiltshire which offers residential treatment, and a further community-based site in Liverpool.
It treats all forms of addiction including alcoholism, drug addiction, gambling addiction, sex addiction and food-related disorders.
(Additional reporting by Rebecca Perring.)
