When Lewis Hamilton joined McLaren back in 2007, he was just a rookie driver. His teammate was Fernando Alonso, a 2-time world champion. In Formula One, your teammate is your biggest rival, and Hamilton and Alonso are prime examples of that.

Their first season as teammates would also be their last. But the Formula One community distinctly remembers how the rookie driver challenged Alonso for the title back in 07′ but ultimately lost it to Kimi Raikkonen.
Hamilton had just joined McLaren as a rookie in 2007. Alonso was looking to defend his championship from his rivals on the grid. So it is understandable if Alonso would be concerned that a talented rookie was coming after his title. What is more interesting is that both had equal points at the end of the 07′ season.

Seeing that Hamilton had joined a British team, there is a possibility of Fernando thinking that the Woking-based outfit could favor one of their own.
An incident that happened between the duo was at the 2007 Hungarian Grand Prix. During the intense qualifying session, Alonso allegedly wasted time in the pit box, so that his teammate couldn’t have enough time to put in a lap time in Q3 of the session.
Another issue Alonso had was the infamous “Spygate” scandal with McLaren. The Spaniard allegedly threatened the then-boss Ron Dennis to reveal documents to the FIA that they had stolen confidential documents from Ferrari.
Before the 07′ season wrapped up, Alonso had announced that he would go back to Renault for the 2008 and 2009 seasons. This brought an end to his partnership with Hamilton at the Woking-based team.