How low can Ryan Reynolds’ voice go?  Thanks to a new TikTok trend, fans almost found that out -- had Will Ferrell not interrupted.

Taking to social media on Monday, the Deadpool star shared a video of him singing MIKA's 2009 hit "Grace Kelly," with Reynolds lowering his voice an octave each time he repeats the chorus.

However, just as Reynolds, 44, begins to flex his vocals for the fourth part, Ferrell bursts in from the background while singing in a playful falsetto.

The Canadian actor whips around and feigns confusion as Ferrell, 54, goes ham on the microphone, shaking his head and closing his eyes as he continues to sing higher.  During one point in the exchange, the Elf star stares at Reynolds, as if to challenge him, before settling back into his high-pitched serenade.

That leads to the two harmonizing beautifully to "Grace Kelly," with Reynolds joking that the final part of the challenge is "acceptance."

"Late to the Grace Kelly TikTok trend but WAY early for our Christmas movie musical," Reynolds joked in the caption.

Several celebrities, including Octavia Spencer and Jeremy Renner, jumped into the comment section to approve of their shenanigans -- in addition to a potential holiday movie starring the two comic legends.

The Grace Kelly Harmony Challenge, which gained traction over the summer, tasks people on TikTok to harmonize the vocals in MIKA's 2009 single and mash it up into one epic cover.

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