This investment has never been secret.
Google (now under parent company Alphabet) invested roughly $900 million as the majority of a ~$1 billion funding round alongside Fidelity Investments. This gave Google an initial equity stake of about 7–7.5% in SpaceX at a valuation of roughly $10–12 billion.
In fact it was often mentioned as a recommended way to try to invest in SpaceX via proxy, before IPO. I don't think that advice had much merit, but it was there nevertheless.
Remember this was also when SpaceX was actually about space, instead of mostly AI and Twitter. Long-term shareholders that were sold on the space, have to be thinking about how to get out once their lockups expire.