The Wikipedia article about The Chronicles of Narnia contains the following statement about Aslan:
C. S. Lewis described Aslan as an alternative version of Jesus as the form in which he may have appeared in an alternative reality.[citation not found]
Reference 28 in the above quote is Walter Hooper's C. S. Lewis: A Companion and Guide, which apparently does not support that statement (or a Wikipedia editor didn't find it due to a missing page number). Reference 29 is an article on LitCharts.com, which may not be a valid source, since it might have used the above Wikipedia article as a source, thereby creating a circular reference.
So where did C. S. Lewis describe Aslan in the way stated above? The source needs to be more specific than the statement that Aslan is an allegory of Jesus.