Malcolm in the Middle star Erik Per Sullivan seen for first time in 18 years in very rare appearance

Ever since 2007, former child actor Erik Per Sullivan has remained out of the spotlight when it comes to being pictured in public.

That is, until last week, when he shocked fans by making an appearance in Boston, being spotted by paparazzi whilst out shopping.

Sullivan shot to fame all the way back in the year 2000, after being cast as 'Dewey' in the much-loved sit-com Malcolm in the Middle.

He appeared on the FOX show for six years alongside his on-screen big brother, Frankie Muniz, who plays the titular character.

Equal Justice actress Jane Kaczmarek and Breaking Bad front-man Bryan Cranston also starred as Malcolm's parents, Lois and Hal, whilst Christopher Kennedy Masterson and Justin Berfield played Sullivan's other brothers, Francis and Reese.

Alongside his television mother Kaczmarek, the child star also wrote an afterword in the children's book Together, inspired by the charitable organisation Heifer International.

The star was photographed this week (The US Sun / News Licensing)

Whilst appearing on Malcolm in the Middle, Sullivan also appeared in a number of film and TV productions - including the 2004 festive flick, Christmas with the Kranks, and independent blockbuster Mo in 2007.

The star was also recognised for having voiced Sheldon the Seahorse in the Disney animated movie Finding Nemo - one of the titular fish's school friends - as well as the accompanying video game.

After not being pictured in public since 2007, he gained his last acting credit in the 2010 teen crime-drama Twelve when he was just 18.

Fans of his original comedy series were heartbroken when he Massachusettes-born star was subsequently absent from all Malcolm in the Middle reunions, with many left concerned for his wellbeing.

However, Sullivan was spotted looking happy on a day out in Boston last week, being photographed carrying some shopping bags.

In the now-viral snaps, he could be seen wrapped up in a thick jumper - which he'd paired with a pair of green trousers and boots.

Sullivan will not appear in this year's reboot (FOX)

According to Kaczmarek, following the success of the show, Dewey turned his attention towards education.

Now aged 33, he is understood to have attended university in the years since his supposed 'disappearance', and is now reportedly studying Victorian Literature as a graduate student.

The actress explained during an appearance at the Paris Manga Sci-Fi Show last year: "He’s very very well.

"He did Malcolm for seven years. He started at 7, he ended at 14. He wasn’t interested in acting at all."

It was announced recently that Sullivan would be the only central cast member that would not return to the big screen for the show's 2025 reboot - despite the fact his four big-name family members would be making a comeback.

The special is scheduled to land on Disney+ later this year, but will see Fargo actor Caleb Ellsworth-Clark playing Dewey - as per Variety.