WARNING: The following contains spoilers for Avengers #51, on sale now from Marvel Comics.
No family is perfect, and many parents keep secrets from their children for as long as they can in an attempt to protect them from harsh truths that could change their perception of themselves or their relatives. Sadly, children will inevitably uncover these secrets one day, and the knowledge that their parents actively hid this information from them usually makes the moment that the truth finally comes out even worse. Situations like these can tear entire families apart in the real world, but in the Marvel universe, they can threaten the safety of the world itself.
Since learning that his father Odin has been hiding the true identity of his birth mother from him his entire life, Thor has been sent on a psychological downward spiral that threatens to tear the Avengers apart. In an attempt to lift his longtime friend's spirits in Avengers #51 (by Jason Aaron, Juan Frigeri, David Curiel, VC's Cory Petit, and Carlos Lao), Iron Man opens up about his own experiences with uncovering the dark secret that his parents had kept from him while he was growing up, and the similarities between their situations prove that no hero comes from a perfect home.
Throughout his childhood, Thor believed that Odin's wife Freyja was his mother, and he's loved her as such well into adulthood. However, during a cataclysmic battle against the Celestials in Thor #300 (by Mark Gurenhold, Ralph Macchio, Keith Pollard, Gene Day, Carl Gafford, and Joe Rosen), Thor "discovered" that his true mother was Gaea, the divine embodiment of the Earth. This revelation sent Thor into a deeply-traumatic identity crisis, but he eventually accepted it and forgave Odin and Freyja's deception. Sadly, Thor's trust in Odin was once again shattered in Avengers #42 (by Aaron, Luca Maresca, Curiel, and Petit) when the cosmic Phoenix revealed herself to be his mother through her first human host, the Avengers 1,000,000 B.C member Firehair, dismissing his supposed relationship with Gaea as another one of Odin's lies.
The revelation that his father had once again lied to him and that his true mother is a being that has massacred entire planets sends Thor into a deep depression that drives him to sever his ties to the Avengers and ban Echo, the Phoenix's latest host, from setting foot in Asgard. Seeing how badly Thor is hurting, Iron Man visits him and admits that he knows what it's like to discover something about your family that causes you to question who you are. Growing up, Iron Man believed that he was the son of Howard and Maria Stark but later learned that he was adopted and that his true parents were Jude and Amanda Armstrong, agents of Hydra and S.H.E.I.L.D respectively. Although Iron Man was able to track down Amanda and make peace with her in International Iron Man #5 (by Brian Michael Bendis, Alex Maleev, Paul Mounts, Clayton Cowles), he's still struggling to accept the fact that he isn't related to the people who raised him.
Before they are cut off by an invasion by the Multiversal Masters of Evil, Iron Man remarks that he's never met heroes who come from happy families, and the simple fact of the matter is that there aren't many who do. The childhoods of many of the Avengers were defined by violence, murder, and conspiracy, from Hawkeye and Hulk's upbringing under abusive fathers to Black Widow's traumatic training within the Red Room Program, and these experiences shaped the heroes that each of them grew up to be more than any of them would like to admit. Although Iron Man and Thor came from more privileged backgrounds than their teammates, both of them struggled to form an emotional bond with their fathers. In turn, Howard and Odin both kept secrets from their sons that would one day wreak havoc on their lives.
Despite his best intentions, Odin's decision to hide his relationship with the Phoenix has brought both Asgard and his relationship with Thor to the brink of ruin. With a new incarnation of the Dark Phoenix barring down on Asgard, Thor's inability to work with Echo could destroy everything that Odin has built, and there may soon be no one alive who Odin can blame but himself.