Sirius C hasn't been proven to exist.
"Hunt for Sirius C and Substellar Companions
According to Duchner and Brown (2000 preprint -- in postscript), three analyses of the proper motion of Sirius found a perturbation in the orbit of
Sirius B with a period around six years (Ch. Volet, 1932; Walbaum and Duvent, 1983; and Benest and Duvent, 1995). The analyses did not resolve whether
the perturbing body orbits Sirius A or B, although dynamical simulations suggest that stable orbits exist around both stars at circumstellar distances
up to more than half the binary system's closest separation of 8.1 AUs (Daniel Benest, 1989). Because ancient astronomers believed that Sirius was
red in color as late as 2,000 years ago, some investigators wonder if the system may have a third stellar component, Sirius C, with about five percent
of Sol's mass that implies a spectral type M5-9 in a six-year elliptical orbit around Sirius A (Benest and Duvent, 1995). A recent search for faint
companions using the Hubble Space Telescope found no supporting evidence for a large Jupiter or brown dwarf sized object, although the observed
positions of Sirius AB -- Gl 244 AB -- differed from published orbital elements (Schroeder et al, 2000)."
here's another site
"Sirius C: Anu
This, the third of the Sirian stellar family, did also ascend from the third dimension at the time of the Sirian shift.
Although the scientific community has not confirmed the existence of Sirius C, the Dogon knew of it by the name, Enome Ya, and they described it too
as revolving around Sirius A.
Of the planets that orbited Anu, one did not achieve ascension when the star, which remains in the fourth dimension, did not: that planet is Nebiru,
the home of the Annunaki.
Nebiru was flung out of Sirius, was captured by our sun, and ricocheted back to Sirius and it is to this day caught between the two star systems, on
an elliptical journey that takes approximately 3,600 years to complete."
Sirius C: Anu