Only 6.2m people tuned in to watch the last episode in the current series of Doctor Who on Saturday night.
Millions watched Doctor Who regenerate
The viewing figures were down on previous episodes of the series, which has been a ratings hit for the BBC.
But a spokeswoman for the BBC said the warm weather was a likely reason for fewer people watching TV indoors.
The final episode saw the Doctor - played by Christopher Eccleston - regenerate into the next Time Lord, David Tennant.
The BBC spokeswoman said that, despite viewing figures being down, it was still the most watched television show of the evening, with a 41.8% share of the audience in the 1900-2000BST slot.
"Almost half of those watching television tuned in to Doctor Who," she said.
"It continues to be the most-watched television show on a Saturday night."
Casanova actor Tennant will become the 10th Doctor Who when the programme returns later this year.
His first words as the Time Lord were: "Hello. Hmm, new teeth. That's weird. Now where were we?"
David Tennant made his debut as the Doctor
Billie Piper will be back for a second series as the Doctor's assistant, Rose Tyler.
Earlier this week the BBC announced there would be a third series in the current run of the drama, written by Russell T Davies.
Almost 3m people also watched Doctor Who: The Ultimate Guide, which preceded Doctor Who at 1815BST.
Beverley Hills Cop attracted an audience of 2.8m when it was broadcast on ITV at 1830BST, and A Picture of Britain pulled in 1.4m on BBC Two at 1845BST.
Just over 1m watched Battle of Britain on Five, while 1.3m tuned in to watch World's Biggest Airliner: Building the Airbus A380 on Channel 4.