James Naughtie has apologised after referring to Caitlyn Jenner as “he” during a discussion on Radio 4′s flagship Today programme.

The US celebrity, formerly known as Bruce, made her debut as a transgender woman called Caitlyn in Vanity Fair earlier this week.

In just four hours she had gained a million followers on Twitter as images of the front cover photoshoot by Annie Leibovitz – showing long-haired Caitlyn in a strapless corset, legs crossed, sitting on a stool – went viral.

Caitlyn has previously talked of preferring the use of “he” but tweeted:

During a discussion on Today, veteran broadcaster James said: “Now, this is complicated. He used to be called Bruce but he’s now a woman.

“I realise some of you will never have heard of Kim Kardashian, let alone her stepfather, who was Bruce and is now a woman but, anyway, they are very well known on television.”

He added: “There’s not a million people going on because they are interested in discussing transgender issues, surely. They are on it because he/she is a celebrity.”

James was criticised on Twitter for referring to Caitlyn as he.

James later apologised on Twitter.