Adele Roberts is running the London Marathon in aid of charity Heads Together, which is supported by Prince William and Catherine.
"Huge thanks to people like Adele," Prince William told hosts Scott Mills and Chris Stark.
The prince also revealed he had previously texted in to Radio 1, under an assumed name.
Along with song requests, he's also asked for - and got - a shout out from former Radio 1 DJ Sara Cox.
Speaking about their mental health campaign, Prince William described how "eye-opening" the experience had been.
"This issue of mental health is really brimming under the surface of public consciousness," he said.
Catherine said she was keen to promote the "power of a simple conversation" when it comes to tackling mental health.
She said young mums she had spoken to in the past had said talking about their feelings could be "like medicine".
Duke and Duchess announce the Official Chart
The Duke and Duchess helped Greg James kick off the Official Chart, with Prince William joking about Harry [Styles] "coming along to spoil Easter" for Ed Sheeran.
"Sounds familiar," he quipped about the other [Prince] Harry.
The pair also revealed there's a Royal Family Whatsapp group.
And they said they watch "a lot" of children's programmes with their children.
"George has gone past Peppa Pig," he said, adding that Fireman Sam was a big hit in their house at the moment.
When it comes to adult programmes, the prince said Game of Thrones "was worth watching".
And they "absolutely" are allowed to order takeaway when it comes to movie night, with Catherine favouring a curry.
Earlier this week Prince William and Lady Gaga joined forces to encourage people to be more open about their struggles with mental health.
The singer, who headlined Coachella Festival on Saturday, had a frank video chat with the Duke of Cambridge from LA.
He'd previously read her open letter about living with post-traumatic stress disorder.
Last week, Prince Harry revealed that he had counselling after his mother Princess Diana's death.
He said he'd spent nearly 20 years "not thinking" about her car crash in Paris in August 1997.