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As of now, there is no official information confirming that Simu Liu (who plays Shang-Chi in the Marvel Cinematic Universe) and Mark Ruffalo (who plays Bruce Banner/Hulk) have discussed or revealed any "secrets" about Marvel's upcoming projects together. However, both actors have been vocal about their roles and the importance of maintaining secrecy around Marvel's storylines. Simu Liu has often emphasized the value of secrecy in the MCU, especially regarding major plot points in Shang-Chi and the Legend of the Ten Rings and its potential connections to future films. Similarly, Mark Ruffalo has spoken about the importance of keeping story details under wraps, especially as The Marvels and other Phase 5 projects unfold. If you're referring to a recent interview, social media post, or teaser that suggests a deeper collaboration or "secret" between the two, it may be a rumor, fan speculation, or a promotional teaser. Always check official sources like Marvel Studios’ social media, press releases, or trusted entertainment news outlets (like Variety, The Hollywood Reporter, or Marvel.com) for verified information. So while there’s no confirmed "secrets safe with Holland and Ruffalo" in a literal sense, both actors are known for respecting the secrecy that surrounds Marvel's storytelling — a tradition that helps preserve the surprise for fans worldwide.