They were accompanied by Motaz Amer, whom they presented the young change maker award to during the ceremony.
The annual event recognises young people who have succeeded against the odds, improved their chances in life and had a positive impact on their local community.
Willoughby donned a yellow dress which featured a cap sleeve and buttons up to her neck for the occasion while Tucci sported a cream suit with a faint check pattern and a darker-toned tie.
Presenting duo Ant McPartlin and Declan Donnelly, Spice Girl Geri Horner, former Strictly Come Dancing dancer Oti Mabuse, singer Sam Ryder, musician Nile Rodgers, and magician Dynamo were among the other celebrity ambassadors who met the King at the event.
Ahead of her royal job, Willoughby appeared on ITV’s This Morning alongside her co-host Phillip Schofield.
Willoughby told This Morning viewers: “I put my posh dress on today because later on this afternoon I am heading to Buckingham Palace and there the King will be, and we get to introduce the award winners to the King so he can say well done, which is all quite exciting isn’t it?”
Schofield, 61, then said he was “holding the fort” before Willoughby, 42, responded with a “thank you”.
Later in the show, as Willoughby departed, they shared an embrace and she told Schofield: “Don’t be naughty… and save me a piece of cake.”
The news comes amid reports of a rift between the pair, who have presented the show together since 2009.
The co-hosts of ITV’s Dancing On Ice have been open about their close friendship over the years, which has included sharing pictures on social media of them while on joint holidays with their families.
After reports of the pair’s relationship coming under strain, last week Schofield said in a statement to The Sun that Willoughby is his “rock”.
He added: “We’re the best of friends – as always, she is an incredible support on screen, behind the scenes and on the phone.
“Holly has always been there for me, through thick and thin. And I’ve been there for her. The last few weeks haven’t been easy for either of us.”
Schofield took pre-planned leave from the show around his brother’s sex abuse trial at Exeter Crown Court last month.
In April, Willoughby also took time off from the ITV morning programme due to having the painful rash shingles, which is caused by the same virus as chickenpox.
Last year, the duo faced a backlash over claims they skipped the queue for the Queen’s lying in state in September.
The chief executive of ITV Dame Carolyn McCall said Schofield and Willoughby had been “misrepresented” over the issue and stressed they had been attending as members of the media to film a segment for This Morning following an online outcry.