It’s an iconic photo that has been used on posters, T-shirts and memorabilia for decades.

Now 50 years after it was taken, the Dundee man behind the camera has told of the night he snapped Frank Zappa on the toilet.

In 1967, a young photographer called Robert Davidson was at a press event for the rock legend at the Royal Garden Hotel in London when the Yankee musician took a comfort break.

Zappa, who was just making a name for himself on the music scene at the time, would go on to become a cult hero for the 60-plus albums that he released — both with his band The Mothers of Invention and also as a solo artist.

Reliving the moment to the Tele, the Dundee-born photographer said he was milling around the hotel room when he came across the rocker, sitting on the toilet with the door wide open taking a call from his wife.

Robert chanced his luck and asked if he could take a picture.

He said: “There was a real buzz about him. When I got there he was wandering around the room.

“It was really hot that day so he took his top off and then said he was going to use the loo.

“I started to wander around the hotel room, looking for somewhere to take a picture and I passed the bathroom.

“The door was open and there he was on the phone talking to his wife. I couldn’t knock on the door because it was open already.

“I just asked him if I could take his picture and he said to his wife ‘there is an English guy wanting to a picture of me on the John’ or whatever Americans call it.

“He then gave me permission to take the pictures.

“It was such an excellent picture. He ended up letting me take 12 of them.

“He basically let me do what I wanted so I took that picture and a few of him on the phone and pulling his trousers up. I also took shots of him sitting in the bidet along with various other pictures.”

Robert said a deal couldn’t be reached for Zappa to play at the Albert Hall in the end — and he ended up not getting paid for the job.

He decided to take the photo and have it made up into a poster.

He added: “I got myself a printing plate made up at a great expense and had 1,000 copies of the poster made and had them put in a few shops.

“They told me they were selling like hot cakes so I had some more printed and I made some money. It was enough to pay off what I had spent to start with.”

However, Robert’s success was short-lived.

The next time that Zappa came into town, his distributors were contacted and asked why a percentage wasn’t going to the artist.

The two parties agreed that 20% of sales would go to Zappa but, three months later, Robert received a call saying the distributors had “forgotten to send the money”.

Robert said the situation got “unsavoury” and he was forced to give up the original negatives.

The poster went on to sell millions of copies — but Robert claims he “never saw a penny”.

It was only after the death of Zappa’s manager Herb Cohen — who left his estate to his record label, who subsequently sold it off — that Robert was contacted and told that the negatives were up for sale on eBay.

He contacted the seller and managed to buy them back — nearly 40 years afterwards.

Robert’s dad was serving in the RAF and was stationed at Leuchars, while his mum lived in Dundee.

Born in the city in 1942, he later moved away but has returned on numerous visits since and says he is “proud to be from Dundee”.

After being expelled from school at the age of 17, a chance meeting with a photographer in Paris led to him becoming one himself.

He returned to England and had a career as a pop group photographer. The 75-year-old now lives in Totness in Devon.

Zappa died in 1993, aged 52.