Lab Rats - Season 4 - Eps 21: And Then There Were Four
Everyone is shocked when Douglas introduces a fourth bionic sibling named Daniel who’s been living a normal life with an adopted family. Daniel later comes to the academy to meet his father, uncle, and cousins. After Daniel's bionics are accidentally activated by the Lab Rats, Donald and Douglas find out what happened they have to come clean to Daniel about his power-replicating abilities. Daniel also finds out that his cousins are actually his biologic siblings. Filled with anger, Daniel goes out for air on the beach, where Leo and him have a conversation about Douglas. Not too long after, Daniel, using Leo's abilities, accidentally causes a leak in the hydro-loop's fuel tank. After Adam and Daniel combined their powers to stop it, Douglas apologizes to Daniel for lying and Daniel decides to give Douglas a second chance.
About Lab Rats

Title: Lab Rats
First Air Date: 2012-02-27
Last Air Date: 2016-02-03
Status: Ended
Rating: 8.111/10 (from 157 votes)
Language: EN
Seasons: 4
Total Episodes: 96
Network: Disney XD
Genres: Comedy, Sci-Fi & Fantasy, Kids
Production Companies: Walt Disney Television, It's a Laugh Productions
Synopsis
Leo is an ordinary teenager who has moved into a high-tech "smart'' house with his mother, inventor stepfather and Eddy, the computer that runs the house. Leo's life becomes less ordinary when, one day, he discovers a secret underground lab that houses three experiments: superhuman teenagers. The trio -- Adam, the strong one, Bree, the fast one and Chase, the smart one -- convinces Leo and his parents to let them leave their lab and join Leo at school, where they try to fit in while having to manage their unpredictable bionic strengths. As Leo figures out a way to keep his new pals' bionic abilities a secret, they help him build self-confidence.
Cast

William Brent
Chase Davenport

Spencer Boldman
Adam Davenport

Kelli Berglund
Bree Davenport

Tyrel Jackson Williams
Leo Dooley

Hal Sparks
Donald Davenport