George Underwood is becoming a little sick of his claim to fame. More than half a century ago, in Bromley, Kent, the 15-year-old Underwood asked Carol Goldsmith out; she said yes, and a date was fixed for the youth club the following Wednesday. But on the day, Underwood’s best friend, David Jones, called him to say that Carol had changed her mind. This wasn’t the case, as it happens. Nor was it true – as Jones later bragged – that he’d got together with Carol.

Underwood “saw red”, as he puts it, and punched Jones once in the left eye. A week later he found out that his fingernail had scratched the eyeball and Jones had been rushed to hospital. For Jones, who underwent two operations and was left with one permanently dilated pupil, it was deeply traumatic; but for David Bowie, the man he would eventually become, this entrancing frozen eyeball – that appeared black, not blue, like his other iris – would become an essential part of his aesthetic.

Underwood is now 69 and his relationship with Bowie survived that teenage scrape – they exchanged birthday presents up until the singer’s death in January – and he is an artist in his own right. In the 1960s and 1970s, he supplied album cover illustrations for T Rex, Procol Harum, Mott the Hoople and Bowie himself. In latter years, his figurative oil paintings, inspired by the Vienna School of Fantastic Realism, have been fixtures of the Royal Academy’s Summer Exhibition. On 3 April, a show of new work and old prints opens at the Imagine Gallery in Suffolk.

“The next painting is always going to be the best one you’ve ever done, isn’t it?” says Underwood. “Hopefully I’ll get it right one day.” He laughs, but there’s an edge. “I’ve been very successful at avoiding fame and fortune! Not like David, you see.”

L-r: Angie Bowie, George Underwood, Birgit Underwood and David Bowie at George Underwood’s wedding in 1971. Photograph: Courtesy George Underwood

The pair were both born in January 1947 and met when, aged nine, they enrolled as Cubs at the 18th Bromley Scouts. They began almost immediately talking about music – a shared love of skiffle and Radio Luxembourg – and both fancied themselves as artists. “I’ve always loved George’s work,” Bowie wrote in 2014. “I think he may well have unconsciously tipped me toward music. Sitting alongside him in art class convinced me (among others) that I would never achieve his fluidity of line. His sense of ‘rightness’ in relation to his subject, whatever it was. I got my dad to advance me the money to buy an alto sax instead.”

Their first band together was the Konrads, with George on vocals and David on saxophone. “He did a couple of vocals, but I didn’t want him to take over,” says Underwood. Then there was the Hooker Brothers, a homage to John Lee Hooker – “a bit strange, these two young white British boys doing black American blues” – and finally the King Bees.

Alongside all these endeavours – on both sides – was an undercurrent of competition. This only intensified when it was Underwood, still a teenager, who was first to sign a record deal: a five-year solo contract with Mickie Most, a producer riding high on the success of Herman’s Hermits. “It looked like I’d just won the X Factor,” Underwood recalls. “I was on Thank Your Lucky Stars, things like that. My record didn’t sell, but it was being played on the radio a lot and I think that must have pissed David off. Well, it did, because I met up with him and he gave me the evil eye… That wasn’t meant to be a pun.”

But it wasn’t to be, for Underwood. Aged 19, he believes his drink was spiked with LSD, leading to a mental breakdown. “I went bonkers,” he says simply. “It’s a difficult one for me to talk about, but I’m glad it happened when it did and it’ll never happen again, that’s for sure.”

The Silence Ahead by George Underwood. Photograph: Courtesy George Underwood

Underwood stopped making music and began to work as an illustrator. An early commission came from Bowie recommending his old friend to Marc Bolan for T Rex’s debut album, My People Were Fair and Had Sky in Their Hair….

Underwood followed that with a surreal drawing for the 1969 album David Bowie, which was reissued in 1972 as Space Oddity. It features a rat in a bowler hat, two astronauts holding a rose, an oversized fish in a lurid Game of Thrones-esque setting. “David did a little sketch for me,” says Underwood. “He knew damn well what he wanted but he thought I was the best person to interpret it for him.”

Underwood is clearly drawn to mythic themes in his art: medieval warriors, angels and giants are recurring subjects. In the early years, he would do oil portraits of celebrities that he admired, from Keith Richards to Muhammad Ali. But these days, he prefers to draw from his imagination. The result is typically lush and deeply textured, with the figures often enigmatically avoiding the viewer’s gaze.

When Bowie died, Underwood couldn’t bring himself to paint. But recently, he has started work again on a series of angels. “I know it sounds a bit cliched, but when [longtime Bowie collaborator] Mick Ronson died, I’d been doing sculptures of angels and I sent some photographs to David,” says Underwood. “And David phoned me up and said: ‘God, they made me cry!’”

Underwood sighs. “So I thought, Oh God, perhaps I’ll paint an angel. Who knows where it all comes from?”

Imagine Gallery, Hall Street, Long Melford, Suffolk. The exhibition runs from 3 April to 7 May