PICTURES show the momentous moment a teacher completed a 1000km marathon on behalf of his student on Saturday ( July 11).

Alasdair Robertson, Assistant Headteacher of Wallington County Grammar School, embarked on a fundraising challenge after his pupil was diagnosed with cancer.

Sachin Shah, 17, was diagnosed with a form of bone cancer called osteosarcoma ( in February) after complaining of a pain in the inside of his right leg.

His teacher, Mr Robertson, was on the way to a ski trip with Sachin, when he received the devastating news from his father about his diagnosis.

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The 17-year-old started his treatment on March 3, less than three weeks before the country went into lockdown.

Over the past few months, Mr Robertson has continued to teach his pupils whilst running 10km per day, for almost 100 days, for cancer charity CLIC Sargent.

See more: Teacher runs 1000km to raise money for pupil with cancer

On Saturday, Sachin and his family gathered at the school grounds to cheer on his teacher as he ran a full marathon to take the total up to 1000km. 

Carshalton and Wallington MP, Elliot Colburn was also in attendance. 

Alasdair Roberston said: "I feel privileged to be helping Sachin and others in his position.

"Finishing at school and having around 200 members of our community, staff, students and alumni show up to support me on my final 5km and when I crossed the finish line was so overwhelming.

"Seeing how much it meant to people, especially Sachin, was undoubtedly one of the best feelings I have had.

"To know that what you are doing is making a difference to young boys and girls who are suffering from cancer is tremendously moving and humbling.

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“The best thing about the day was seeing Sachin's smile as I crossed the line, it made all the effort of running 1000km in 100 days feel more than worth it.

"I can only thank everyone who showed up and has so generously donated after being inspired by Sachin's resilience, toughness and positivity."

Children's cancer charity, CLIC Sargent have been supporting Sachin since his diagnosis.

Rose Bailey, CLIC Sargent’s Fundraising and Engagement Manager for Surrey, said: “It’s been such a pleasure supporting Ali during this incredible challenge.

"We are completely in awe of his enthusiasm and determination.

"We are so grateful to him for raising money for CLIC Sargent, and ensuring we can continue to be there for young people facing cancer.

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"Sachin is clearly a very popular and talented young man and Ali is a much-loved teacher.

"It was amazing to cheer Ali on as he crossed the finish line, along with his colleagues, friends and family."

Sachin has recently had surgery on his knee and is currently on the fourth cycle of his chemotherapy treatment.

He hopes to study mathematics at either Oxford or Cambridge University.

Donations reached £19,355 out of the targeted £15,000 at the time of publishing.

To donate visit at: https://www.justgiving.com/fundraising/alasdair-robertson7