3rd LTM in Cluster - Different HW model

I am planning to add a new F5 to our F5 LTM cluster in our DR (secondary) DC.

I have got F5 BIG IP 2K in the cluster and now want to add a BIG IP 4K series to the cluster.

Is there any documentation/articles to add the 3rd LTM which is a different hardware model and also how we can get it added to the cluster.

Will the new F5 be able to talk to the GTMs in both primary and secondary DC?

Jess