Catherine's dress was paired with plum, velvet Jimmy Choo heels while her gold earrings also by Erdem matched her simple clutch.
The pair attended the first Global Ministerial Mental Health Summit, an initiative that's been launched to raise awareness of mental health issues around the world.
However, proving that even princesses have off-days, we have to say we're not too sure about her latest attire.
Another policy up for discussion is a declaration committing to putting mental health on an equal footing with physical health.
The Duke and Duchess viewed the work of contemporary fine artist Dario Vargas, who had painted an original piece for the event.
Prince William joked that the painting had been ruined.
This saw the couple break out into laughter along with the crowd.
The royal couple arrived to attend multiple presentations on case studies of active mental health programs and also met with young people to speak about their experiences with mental health.
The project's founder Dixon Chibanda said: "Bringing our Friendship Bench to London helps show leaders and campaigners how we can all empower communities to tackle the global gap between mental health problems and the treatments available".
It's their first joint public engagement since Prince Louis' birth.
The royal donned a chic lilac Emilia Wickstead dress, which she teamed with a pair of pointed nude stilettos and a matching handbag.
Last month Prince William opened up about the emotional toll of witnessing suffering during his time as an air ambulance pilot.
Erdem is a much beloved designer of the royals, with speculation around whether the brand has designed Princess Eugenie's wedding dress for her nuptials on Friday.
11 October 2018
11 October 2018
11 October 2018
11 October 2018
11 October 2018
