Amazing footage of a teenager surprising his step-dad with official adoption papers.

The video, filmed on September 2, shows Damian, 18, giving Robert Mitten the adoption papers on his 40th birthday, and his reaction is amazing.

Damian's mother later wrote online: "My husband Robert Mitten has been taking care of my son Damian since he was two-years-old.

"His biological dad left the picture since he was that little and Robert has been taking care of him since then as his own."

"It took us a long time to do the adoption process because we weren't sure if the biological father would pop his head back in to cause more of a set back so we thought it was best to wait until Damian was 18," she continued.

"Damian always wanted Rob as his father because that's all he knew growing up.

"Damian turned 18 in August and with the help of my family and Rob's family (secretly pitching in the funds for the adoption) the family was able to get together for Rob's 40th birthday on September 2nd to surprise him. It's been a very long wait but we finally made it happen.

"It means everything to us."