Billy in CR 838:
If I remember correctly, yes, the Earth's moon came here about 25 million years ago and settled around the Earth, but one star was 'nudged' away from the Earth's orbit, which today …
https://www.futureofmankind.co.uk/Billy_Meier/Contact_Report_838

Please note:
In the given context the word ‘star’ is a misleading translation of the German “Gestirn”:
A more fitting translation would be ‘celestial body’.
As for which ‘celestial body’ this could have been:
Mercury (diameter: 4880 km) is approx. the size of our present-day moon (diameter: 3474 km)
So maybe it was Mercury that was once our moon.

Further details about the moon can be found

Semjase and Quetzal explain in great detail how the Destroyer (large planet) and our present-day Moon (fragment of a planet created by the Destroyer colliding with a planet) originated out of a faraway collapsing sun system from the Lyra System some 25 million years ago and how they found their way to our SOL system. According to Quetzal the planet fragment became a part of our SOL system “a few million years ago" (CR 150:479) whereas Billy (in CR 838) mentions 25 million years ago:
Maybe this is 2.5 million years ago?
(If my memory is right then due to similarities in the sign language used for telepathic transmission of CR texts, the time measurements sometimes are coming out as multiplied by (multiples of) the factor of 10)

Our scientists are still believing the moon is the leftover of another planet colliding with earth billions of years ago. But I wonder how they can believe that if they would consider that two planets colliding together would likely completely destroy both planets or a glancing blow would not cause them to stay in orbit with each other.

6 days later

Yes, Hugo, our scientists ...
_They argue that the composition of the Moon is similar to Earth's mantle. And yes, the isotopic ratios of some elements (e.g., Oxygen) are very similar. But there are subtle differences in isotopic ratios for some elements (e.g., Tungsten/Potassium) which may point to different processes of planetary differentiation*). But these considerations are - more or less - dismissed. So, it may well be that they only consider a different origin once they explore the Moon in more depths.

*) "Planetary Differentiation"
"When planets begin to melt, the materials in them begin to separate from one another. The heaviest materials, such as metallic iron, sink to form cores. Low-density magmas rise, forming crusts. This process is called differentiation..."_
https://www.nasa.gov/stem-ed-resources/differentiation.html