The younger brother of Florida high school shooter Nikolas Cruz has been spotted out for the first time since the deadly massacre as he took to the streets on his skateboard.

Zachary Cruz, 18, was seen skateboarding shirtless near his home in Lake Worth in southern Florida on Friday.

The teenager had been undergoing psychiatric evaluation at a mental hospital in Palm Beach in the days after his 19-year-old brother killed 17 former classmates and teachers at Marjory Douglas Stoneman High School in Parkland on February 14.

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Zachary Cruz, the 18-year-old brother of Florida high school gunman Nikolas Cruz, was seen skateboarding near his home in Lake Worth in southern Florida on Friday

Zachary and his brother, who were both adopted as babies, had not been living together in the lead up to the deadly rampage.

They had been taken in by family friend Rocxanne Deschamps after their adoptive mother Lynda Cruz died from pneumonia in November.

Nikolas moved out in January after being told he could not have guns at the house.

Their adoptive father Roger died when they were small boys.

It emerged at the weekend that Zachary had allegedly bullied his older brother and that the pair had a tumultuous relationship.

Their mother often forced Zachary to take his brother along when he was going out because Nikolas was socially awkward and had a hard time making friends.

The teen, who turned 18 last week, had been undergoing psychiatric evaluation at a mental hospital in the days after his brother's deadly massacre

Zachary reportedly told police after the shooting that he had bullied his older brother and that he deeply regretted it

Zachary and his brother, who were both adopted as babies, had not been living together in the lead up to the deadly rampage

Zachary told Palm Beach sheriff's deputies that he and his friends had often picked on Nikolas and that he deeply regretted it, the Sun Sentinel reports.

The deputy wrote in his report that 'Zachary wishes that he had been 'nicer' to his brother' and that there might have been resentment between the brothers because 'Nikolas may have been the favored brother'.

A Facebook account that is run under Zachary Cruz's name posted a thank you message on Saturday, saying: 'Appreciate all the positive messages'.

Another post on Monday simply said 'reminiscing' alongside a photo of them as young boys.

Nikolas remains locked up at the Broward County Jail after being charged with 17 counts of premeditated murder.

The brothers are pictured above holding the ashes of their adoptive mother Lynda Cruz who died from pneumonia in November

A Facebook account that is run under Zachary Cruz's name posted a thank you message on Saturday, saying: 'appreciate all the positive messages'

A large, dark green Chevy truck was in the driveway

There is also a pastel golf cart at the home where Zachary was spotted

He wore Nike shorts, Nike socks and Nike shoes for the skate around