Nick Grimshaw has recorded the lowest listening figures for BBC Radio 1's breakfast show since records began.
The DJ, who took over the slot from Chris Moyles in 2012, saw his audience drop below five million listeners per week in the third quarter of this year.
The show recorded 4.93 million weekly listeners between July and September - down from 5.5 million last quarter.
Controller Ben Cooper defended the stats and said it was still "the most relevant youth brand in the UK today".
He also said there was still a 10.5 million weekly listenership across the station and that Radio 1 had 9.4 million subscribers on social media, with an additional five million on YouTube.
Listening figures for all stations are traditionally lower in the summer months - but Grimshaw's figures are the lowest for any Radio 1 breakfast show since audience research body Rajar began collecting data.
A source at Radio 1 said: "Grimmy is the number one breakfast show in the UK for young audiences and that's all they really care about.
"Teens are addicted to their phones so you can see why Radio 1 does so well on YouTube and Facebook."
There was better news for Radio 1's sister station - with A.Dot giving BBC Radio 1Xtra its highest ever audience for its breakfast show. It recorded 390,000 listeners in the last quarter - up 33,000 on the previous three months.
People aged between 15-24 listened to just over 14 hours of radio per week last year - seven hours less than the average adult, and 15% less than they did a decade earlier, according to broadcasting regulator Ofcom.
- Roman Kemp's Capital London breakfast show increased its audience - posting 1.11 million in the third quarter. The results were up by nearly 30,000 on the previous three months - it was the first full quarter he's presented the show, after becoming host in May this year.
- Chris Moyles's Radio X breakfast show has also grown its listenership, pulling in almost 75,000 more listeners across the same period, giving it a new weekly reach of 823,000.
- Radio 2 had cause to celebrate after Ken Bruce achieved a record weekly reach of 8.7 million, up from 8.3 million in the second quarter.
- Chris Evans's BBC Radio 2 breakfast show attracted 9.35 million listeners a week in the third quarter of this year, up from 9.01 million in the second quarter.
- BBC Radio 4's Today programme saw a drop in its audience after enjoying a huge growth last quarter. The flagship news programme had 7.06 million listeners a week in the third quarter, dipping from the 7.66 million a week figure it achieved in the second quarter.
- Digital station BBC Radio 6 Music attracted a record 2.4 million listeners a week in the third quarter of the year, an increase from 2.2 million in the second quarter and 2.3 million last year.
- New station Heart 80s, which was launched in March, reached 1.08m listeners per week, up from its maiden quarter by more than 230,000 listeners.